SYNOPSIS

ddpt [bpt=BPT[,OBPC]] [bs=BS] [cdbsz={6|10|12|16|32}] [coe={0|1}] [coe_limit=CL] [conv=CONVS] [count=COUNT] [delay=MS[,W_MS]] [ibs=IBS] [id_usage=LIU] if=IFILE [iflag=FLAGS] [intio={0|1}] [iseek=SKIP] [ito=ITO] [list_id=LID] [obs=OBS] [of=OFILE] [of2=OFILE2] [oflag=FLAGS] [oseek=SEEK] [prio=PRIO] [protect=RDP[,WRP]] [retries=RETR] [rtf=RTF] [rtype=RTYPE] [seek=SEEK] [skip=SKIP] [status=STAT] [to=TO] [verbose=VERB] [--help] [--odx] [--verbose] [--version] [--wscan] [--xcopy]

For comparison here is the synopsis for GNU's dd command:

dd [bs=BS] [cbs=CBS] [conv=CONVS] [count=COUNT] [ibs=IBS] [if=IFILE] [iflag=FLAGS] [obs=OBS] [of=OFILE] [oflag=FLAGS] [seek=SEEK] [skip=SKIP] [status=STAT] [--help] [--version]

DESCRIPTION

Copies data between files or simply reads data from a file. This utility is specialized for "files" that are storage devices, especially those that can use the SCSI command sets (e.g. SATA and SAS disks). It can issue SCSI commands in pass-through ("pt") mode. Similar syntax and semantics to the Unix dd(1) command.

For comparison, the SYNOPSIS section above shows both the ddpt command line options followed by GNU's dd(1) command line options. Broadly speaking ddpt can be considered a super-set of dd. See the section on DD DIFFERENCES for significant differences between ddpt and dd.

This utility either does direct copies, based on read-write sequences, or offloaded copies. In an offloaded copy the data being copied does not necessarily pass through the memory of the the machine originating the copy operation; this can save a significant amount of time and lessen CPU usage.

When doing a direct copy, this utility breaks the copy into segments since computer RAM is typically a scarce resource. First it reads in BPT*IBS bytes from IFILE (or less if near the end of the copy) into a copy buffer. In the absence of the various options and conditions that bypass the write operation, the copy buffer is then written out to OFILE. The copy process continues working its way along IFILE and OFILE until either COUNT is exhausted, an end of file is detected, or an error occurs. If IBS and OBS are different, ddpt restricts the value of OBS such that the copy buffer is an integral number of output blocks (i.e. (((IBS * BPT) % OBS) == 0) ). In the following descriptions, "segment" refers to all or part of a copy buffer.

The term "pt device" is used for a pass-through device to which SCSI commands like READ(10), WRITE(10) or POPULATE TOKEN may be sent. A pt device may only be able to process SCSI commands in which case the "pt" flag is assumed. The ability to recognize such a pt only device may vary depending on the operating system (e.g. in Linux /dev/sg2 and /dev/bsg/3:0:1:0 are recognized). However if a device can process either normal UNIX read()/ write() calls or pass-through SCSI commands then the default is to use UNIX read()/write() calls. That default can be overridden by using the "pt" flag (e.g. "if=/dev/sdc iflag=pt"). When pt access is specified any partition information is ignored. So "if=/dev/sdc2 iflag=pt skip=3" will start at logical block address 3 of '/dev/sdc'. As a protection measure ddpt will only accept that if the force flag is also given (i.e. 'iflag=pt,force').

This utility supports two types of offloaded copies. Both are based on the EXTENDED COPY (XCOPY or xcopy) family of SCSI commands. The first uses the XCOPY(LID1) command to do a disk to disk copy. LID1 stands for List IDentifier length of 1 byte and the command is described in the SPC-4 drafts and the earlier SPC-3 and SPC-2 standards. Recent SPC-4 drafts have added the XCOPY(LID4) sub-family of copy offloaded commands. There is a subset of XCOPY(LID4), specialized for offloaded disk to disk copies, that is known by the market name: ODX. In the descriptions below "xcopy" refers to copies based on XCOPY(LID1) while "odx" refers to either full or partial ODX copies. See the XCOPY and ODX sections below for more information.

OPTIONS

The dd-like options with the name=value syntax are listed first, sorted by name. Following that, options starting with "-" are listed.

bpt=BPT[,OBPC]

where BPT is Blocks Per Transfer. A direct copy is made up of multiple transfers, each first reading BPT input blocks (i.e. BPT * IBS bytes) from IFILE into the copy buffer and then from that copy buffer writing (BPT * IBS) / OBS output blocks to OFILE. This continues until the copy is finished, with the last transfer being potentially shorter. The default BPT value varies depending on IBS. When IBS < 8, BPT is 8192; when IBS < 64, BPT is 1024; when IBS < 1024, BPT is 128; when IBS < 8192, BPT is 16; when IBS < 32768, BPT is 4; else BPT defaults to 1. If BPT is given as 0 it is treated as the default value. For "bs=512", BPT defaults to 128 so that 64 KiB (or less) is read from IFILE into the copy buffer. This option is treated differently in ODX and is typically only needed for testing; see ODX section.
The optional OBPC (Output Blocks Per Check) argument controls controls the granularity of sparse writes, write sparing and trim checks. The default granularity is the size of the copy buffer (i.e. BPT * IBS bytes). That can be reduced by specifying OBPC. The finest granularity is when OBPC is 1 which implies the unit of each check is OBS bytes. When OBPC is 0, or not given, the default granularity is used. Large OBPC values are rounded down so that OBPC*OBS does not exceed the size of the copy buffer.
odx: may be used to limit the data represented by each ROD. Mainly for testing.

bs=BS

where BS is the IFILE and OFILE block size in bytes. Conflicts with either the "ibs=" or "obs=" options. The value of BS is placed in IBS and OBS. If IFILE or OFILE is a "pt" device then BS must be the logical block size of the device. See the DD DIFFERENCES section below. The default is 512 bytes; note that newer disks use 4096 byte blocks with perhaps larger block sizes coming in the future. CD/DVD/BD media use a logical block size of 2048 bytes.

cdbsz={6|10|12|16|32}

size of SCSI READ and/or WRITE commands issued to pt devices. The default is 10 byte SCSI command blocks unless calculations indicate that a 4 byte block number may be exceeded or BPT is greater than 16 bits (i.e. more than 65535 blocks), in which case it defaults to 16 byte SCSI commands.

coe={0|1}

set to 1 for continue on error. Applies to errors on input and output for pt devices but only on input from block devices or regular files. Errors on other files will stop ddpt. Default is 0 which implies stop on any error. See the 'coe' flag for more information.

coe_limit=CL

where CL is the maximum number of consecutive bad blocks stepped over due to "coe=1" on reads before the copy terminates. The default is 0 which is implies no limit. This option is meant to stop the copy soon after unrecorded media is detected while still offering "continue on error" capability for infrequent, randomly distributed errors.

conv=CONVS

see the CONVERSIONS section below.

count=COUNT

copy COUNT input blocks from IFILE to OFILE. If this option is not given (or COUNT is '-1') then the COUNT may be deduced from either IFILE or OFILE. See the COUNT section below.
odx: if a gather list is given to skip=SKIP or a scatter list is given to seek=SEEK then typically count=COUNT should not be supplied. This is because a scatter gather list implies a transfer count. If both are given then ddpt will exit if they are unequal, the force option can be used to override this action.

delay=MS[,W_MS]

after each segment is copied (typically every (IBS * BPT) bytes) a delay (sleep) of MS milliseconds is performed. The default value for MS is 0 which implies no delay. If W_MS is given and greater than 0 (its default value) then there is an additional delay of W_MS milliseconds associated with each actual write operation that is performed. If MS is greater than 0 then there is not a delay before the first copy segment (or after the last); if W_MS is greater than 0 then there is not a delay before the first write segment. These delays can be used for a bandwidth limiting.
odx: the MS delay is implemented in the same fashion after each ROD is copied, apart from the last. If W_MS is greater than 0 then that delay occurs before each WUT command, apart from the first.

ibs=IBS

where IBS is the IFILE block size in bytes. The default value is BS or its default (512). Conflicts the "bs=" option (i.e. giving both "bs=512 ibs=512" is considered a syntax error).

id_usage=LIU

xcopy: SCSI EXTENDED COPY parameter list LIST ID USAGE field is set to LIU. The default value is 0 or 2 . LIU can be a number between 0 and 3 inclusive or a string. The strings can be either: 'hold' for 0, 'discard' for 2 or 'disable' for 3.

if=IFILE

read from IFILE. This option must be given (apart from one odx case). If IFILE is '-' then stdin is read. Starts reading at the beginning of IFILE unless SKIP is given.
odx: the rtf=RTF option may replace the if=IFILE option as input. See the ODX section.

iflag=FLAGS

where FLAGS is a comma separated list of one or more flags outlined in the FLAGS section below. These flags are associated with IFILE and are mostly ignored when IFILE is stdin.

intio={0|1}

set to 1 for allow signals (SIGINT, SIGPIPE and SIGUSR1 (or SIGINFO)) to be received during IO from IFILE or IO to OFILE or OFILE2. Default is 0 which causes these signals to be masked during IO operations with a check for signals prior each IO. As long as IO operations don't lock up (e.g. SCSI READ and WRITE commands) the default is the safer option. Even if IO operations do lock up it is best to let the kernel take care of that.

iseek=SKIP

start reading SKIP blocks (each of IBS bytes) from the start of IFILE. Default is block 0 (i.e. start of file). This option is a synonym for skip=SKIP, see its description.

ito=ITO

odx: ITO is the inactivity timeout whose units are seconds. The default value is 0 which means the copy manager will take the default inactivity timeout value from the Block Device ROD Token Limits descriptor in the Third Party Copy VPD page. ITO is ignored if it it exceeds the maximum inactivity timeout value in the same descriptor (unless the force flag is given).

list_id=LID

LID is the xcopy LIST IDENTIFIER field. It is used to associate an originating xcopy command with follow-up commands such as RECEIVE ROD TOKEN INFORMATION. If given, the LID should not clash with any other xcopy LID currently in use on this I_T nexus.
xcopy: LID is a 1 byte (8 bit) value whose default value is 1 or, if id_usage=disable, 0 . LID must not exceed 255.
odx: LID is a 4 byte (32 bit) value whose default value is 257 (i.e. 0x101) and, if a second default is needed, 258 (0x102) is used. If a clash is detected on the default list identifier value then the next higher value is tried (stopping after 10 attempts).

obs=OBS

where OBS is the OFILE block size in bytes. The default value is BS or its default (512). Conflicts the "bs=" option (e.g. giving both "bs=512 obs=512" is considered a syntax error). If OBS is given then it has the following restriction: the integer expression (((IBS * BPT) % OBS) == 0) must be true. Stated another way: the copy buffer size must be an integral multiple of OBS. If of2=OFILE2 is given then OBS is its block size as well.

of=OFILE

write to OFILE. The default value is /dev/null . If OFILE is '-' then writes to stdout. If OFILE is /dev/null then no actual writes are performed. If OFILE is '.' (period) then it is treated the same way as /dev/null . If OFILE exists then it is _not_ truncated unless "oflag=trunc" is given. See section on DD DIFFERENCES.
odx: if this option (of=OFILE) is not given and the rtf=RTF option is given then the RTF file may be thought of as receiving the output in the form of one or more ROD Tokens. See the ODX section.

of2=OFILE2

write output to OFILE2. The default action is not to do this additional write (i.e. when this option is not given). OFILE2 is assumed to be a regular file or a fifo (i.e. a named pipe). OFILE2 is opened for writing and is created if necessary. If OFILE2 is a fifo (named pipe) then some other command should be consuming that data (e.g. 'md5sum OFILE2'), otherwise this utility will block. The write to OFILE2 occurs before the write to OFILE and prior to sparse writing and write sparing logic. So everything read is written to OFILE2.

oflag=FLAGS

where FLAGS is a comma separated list of one or more flags outlined in the FLAGS section. These flags are associated with OFILE and are ignored when OFILE is /dev/null, '.' (period), or stdout.

oseek=SEEK

start writing SEEK blocks (each of OBS bytes) from the start of OFILE. Default is block 0 (i.e. start of file). This option is a synonym for seek=SEEK, see its description.

prio=PRIO

xcopy: SCSI EXTENDED COPY parameter list PRIORITY field is set to PRIO. The default value is 1 .

protect=RDP[,WRP]

where RDP is the RDPROTECT field in SCSI READ commands and WRP is the WRPROTECT field in SCSI WRITE commands. The default value for both is 0 which implies no additional protection information will be transferred. Both RDP and WRP can be from 0 to 7. If RDP is greater than 0 then IFILE must be a pt device. If WRP is greater than 0 then OFILE must be a pt device. See the PROTECTION INFORMATION section below.

retries=RETR

sometimes retries at the host are useful, for example when there is a transport error. When RETR is greater than zero then SCSI READs and WRITEs are retried on error, RETR times. Default value is zero. Only applies to errors on pt devices.

rtf=RTF

odx: where RTF is a filename. One or more ROD tokens are written to RTF during a read to tokens variant or a full copy variant. One or more ROD tokens are read from RTF during a write from token variant. This option is not required on a full copy variant. ROD Tokens are 512 bytes long and an extra 8 byte (big-endian) integer containing the 'number of bytes represented' is placed after each ROD Token if rtf_len is given.

rtype=RTYPE

odx: where RTYPE is the ROD Type. The default value (0) indicates that the copy manager (in the source) decides. RTYPE can be a decimal number, a hex number (prefixed by 0x or with a "h" appended) or one of "pit-def", "pit-vuln", "pit-pers", "pit-any" or "zero". The final truncated word can be spelt out (e.g. "pit-vulnerable"). The "pit-" prefix is a shortening of "point in time" copy. The "zero" causes a special Block device zero Token to be created.

seek=SEEK

start writing SEEK blocks (each of OBS bytes) from the start of OFILE. Default is block 0 (i.e. start of file). The SEEK value may exceed the number of OBS-sized blocks in OFILE.
odx: SEEK can be a scatter list: comma separated, in the form seek=A1,N1[,A2,N2...] . The scatter list may alternatively be read from a file using this form: seek=@<filename> or read from stdin using this form: seek=- (or seek=@-) . A<n> and N<n> are decimal (optionally with a suffix multiplier) unless a hex indication is given. Hex values are indicated by either a leading "0x" or a trailing "h". The address (i.e. A<n>) is a 64 bit unsigned integer while the number of blocks (i.e. N<n>) is a 32 bit integer. Thus for a block size of 512 bytes, a single scatter gather list element cannot exceed 4 TB ((2**32 - 1) * 512). Note that COUNT is a 64 bit unsigned integer and thus does not have this restriction. There can be no more than 128 scatter list elements.

skip=SKIP

start reading SKIP blocks (each of IBS bytes) from the start of IFILE. Default is block 0 (i.e. start of file). The SKIP value must be less than the number of IBS-sized blocks in IFILE.
odx: SKIP can be a gather list: comma separated, in the form skip=A1,N1[,A2,N2...] . The gather list may alternatively be read from a file using this form: skip=@<filename> or read from stdin using this form: skip=- . See the odx section of the seek=SEEK option for further details.

status=STAT

the STAT value of 'noxfer' suppresses the throughput speed and the copy time reporting at the end of the copy. A STAT value of 'none' additionally suppresses the records in and out reporting after the copy. So 'status=none' makes ddpt act like a traditional Unix command in which "no news is good news". The default action of ddpt is to show the throughput (in megabytes per second) and the time taken to do the copy after the "records in" and "records out" lines at the end of the copy. As a convenience the value 'null' is accepted for STAT and does nothing.

to=TO

odx, xcopy: where TO is am xcopy originating command timeout in seconds. The default value is 0 which is converted internally to 600 seconds (10 minutes). Best to set this timeout value well above the expected copy time. In a odx full copy this timeout is applied to both the POPULATE TOKEN and WRITE USING TOKEN commands.

verbose=VERB

as VERB increases so does the amount of debug reporting sent to stderr. Default value is zero which yields the minimum amount of debug reporting. A value of 1 reports extra information that is not repetitive. A value 2 reports cdbs and responses for SCSI commands that are not repetitive (i.e. other that READ and WRITE). Error processing is not considered repetitive. Values of 3 and 4 yield reporting for all SCSI commands, plus Unix read() and write() calls, so there can be a lot of output. If VERB is "-1" then reporting that would have been sent to stderr is redirected to /dev/null essentially throwing it away.

-h, --help

reports usage message then exits.

-o, --odx

indicates to this utility that one of the four odx variants is requested. See ODX section.

-v, --verbose

equivalent of verbose=1. If --verbose appears twice then that is equivalent to verbose=2. Also -vv is equivalent to verbose=2.

-V, --version

reports version number information then exits.

-w, --wscan

this option is available in Windows only. It lists storage device names and the corresponding volumes, if any. When used twice it adds the "bus type" of the closest transport (e.g. a SATA disk in a USB connected enclosure has bus type USB). When used three times a SCSI adapter scan is added. When used four times only a SCSI adapter scan is shown. See EXAMPLES section below and the README.win32 file.

-x, --xcopy

this option will attempt to call the SCSI EXTENDED COPY(LID1) command. In the absence of another indication the xcopy command will be sent to the destination (i.e. OFILE). See the section on ENVIRONMENT VARIABLES below.

COUNT

When the count=COUNT option is not given (or COUNT is '-1') then an attempt is made to deduce COUNT as follows.

When both or either IFILE and OFILE are block devices, then the minimum size, expressed in units of input blocks, is used. When both or either IFILE and OFILE are pass-through devices, then the minimum size, expressed in units of input blocks, is used.

If a regular file is used as input, its size, expressed in units of input blocks (and rounded up if necessary) is used. Note that the rounding up of the deduced COUNT may result in a partial read of the last input block and a corresponding partial write to OFILE if it is a regular file. After a regular file to regular file copy the length of OFILE will be the same as IFILE unless OFILE existed and its length was already greater than that of IFILE. To get a copy like the standard Unix cp command, use oflag=trunc with ddpt.

The size of pt devices is deduced from the SCSI READ CAPACITY command. Block device sizes (or their partition sizes) are obtained from the operating system, if available.

If skip=SKIP or skip=SEEK are given and the COUNT is deduced (i.e. not explicitly given) then that size is scaled back so that the copy will not overrun the file or device.

If COUNT is not given and IFILE is a fifo (and stdin is treated as a fifo) then IFILE is read until an EOF is detected. If COUNT is not given and IFILE is a /dev/zero (or equivalent) then zeros are read until an error occurs (e.g. file system full).

If COUNT is not given and cannot be deduced then an error message is issued and no copy takes place.

CONVERSIONS

One or more conversions can be given to the "conv=" option. If more than one is given, they should be comma separated. ddpt does not perform the traditional dd conversions (e.g. ASCII to EBCDIC). Recently added conversions inherited from GNU's dd overlap somewhat with the some of ddpt flags.

fdatasync

equivalent to "oflag=fdatasync". Flushes data associated with the OFILE to storage at the end of the copy. This conversion is for compatibility with GNU's dd.

fsync

equivalent to "oflag=fsync". Flushes data and meta-data associated with the OFILE to storage at the end of the copy. This conversion

no_del_tkn

equivalent to "oflag=no_del_tkn".

noerror

this conversion is very close to "iflag=coe" and is treated as such. See the "coe" flag. Note that an error on a block device or regular file OFILE will stop the copy.

notrunc

this conversion is accepted for compatibility with dd and ignored since the default action of this utility is not to truncate OFILE.

null

has no affect, just a placeholder.

resume

See "resume" in the FLAGS sections for more information.

rtf_len

equivalent to "oflag=rtf_len".

sparing

See "sparing" in the FLAGS sections for more information.

sparse

FreeBSD's dd supports "conv=sparse" and now GNU's dd does as well so the same syntax is supported in ddpt. See "sparse" in the FLAGS sections for more information.

sync

is ignored by ddpt. With dd it means supply zero fill (rather than skip) and is typically used like this "conv=noerror,sync" to have the same functionality as ddpt's "iflag=coe".

trunc

if OFILE is a regular file then truncate it prior to starting the copy. See "trunc" in the FLAGS section.

FLAGS

A list of flags and their meanings follow. The flag name is followed by one or two indications in square brackets. The first indication is either "[i]", "[o]" or "[io]" indicating this flag is active for the IFILE, OFILE or both the IFILE and the OFILE. The second indication contains some combination of "reg", "blk" "pt", "odx", or "xcopy". These indicate whether the flag applies to a regular file, a block device (accessed via Unix read() and write() commands, a pass-through device, an ODX offloaded copy or a XCOPY(LID1) offloaded copy respectively. Other special file types that are sometimes referred to are "fifo" and "tape".

append [o] [reg], [io] [odx]

causes the O_APPEND flag to be added to the open of OFILE. For regular files this will lead to data being appended to the end of any existing data. Conflicts the seek=SEEK option. The default action of this utility is to overwrite any existing data from the beginning of OFILE or, if SEEK is given, starting at block SEEK. Note that attempting to 'append' to a device file (e.g. a disk) will usually be ignored or may cause an error to be reported.
odx: if the rtf=RTF option is given, RTF exists, is a regular file and this utility wants to write to RTF then new ROD Tokens are appended to RTF. The default action is to truncate RTF before new ROD Tokens are written to it.

block [io] [pt]

pass-through file opens are non-blocking by default and may report the pt device is busy. Use this flag to open blocking so utility may wait until another process locking (or with an exclusive open) is complete before continuing.

cat [io] [xcopy]

xcopy: set CAT (residual data handling) bit in EXTENDED COPY(LID1) parameter list segment descriptor header. May appear in either flag list when xcopy is being used. Works with the PAD bit for handling residual data on the destination side. See the XCOPY section below.

coe [io] [pt], [i] [reg,blk]

continue on error. 'iflag=coe oflag=coe' and 'coe=1' are equivalent. Errors occurring on output regular or block files will stop ddpt. Error messages are sent to stderr. This flag is similar to 'conv=noerror,sync' in the dd(1) utility. Unrecovered errors are counted and reported in the summary at the end of the copy.

This paragraph concerns coe on pt devices. A medium, hardware or blank check error during a read operation will will cause the following: first re-read blocks prior to the bad block, then try to recover the bad block (supplying zeros if that fails), and finally re-read the blocks after the bad block. A medium, hardware or blank check error while writing is reported but otherwise ignored. SCSI disks may automatically try and remap faulty sectors (see the AWRE and ARRE in the read write error recovery mode page (the sdparm utility can access these attributes)). If bad LBAs are reported by the pass-through then the LBA of the lowest and highest bad block is also reported.

This paragraph concerns coe on input regular files and block devices. When a EIO or EREMOTEIO error is detected on a normal segment read then the segment is re-read one block (i.e. IBS bytes) at a time. Any block that yields a EIO or EREMOTEIO error is replaced by zeros. Any other error, a short read or an end of file will terminate the copy, usually after the data that has been read is written to the output file.

dc [io] [blk,pt]

xcopy: set DC (destination counter) bit in EXTENDED COPY(LID1) parameter list segment descriptor header. May appear in either flag list when xcopy is being used.

direct [io] [reg,blk]

causes the O_DIRECT flag to be added to the open of IFILE and/or OFILE. This flag requires some memory alignment on IO. Hence user memory buffers are aligned to the page size. May have no effect on pt devices. This flag will bypass caching/buffering normally done by block layer. Beware of data coherency issues if the same locations have been recently accessed via the block layer in its normal mode (i.e. non-direct). See open(2) man page.

dpo [io] [pt]

set the DPO bit (disable page out) in SCSI READ and WRITE commands. Not supported for 6 byte cdb variants of READ and WRITE. Indicates that data is unlikely to be required to stay in device (e.g. disk) cache. May speed media copy and/or cause a media copy to have less impact on other device users.

errblk [i] [pt] [experimental]

attempts to create or append to a file called "errblk.txt" in the current directory the logical block addresses of blocks that cannot be read. The first (appended) line is "# start <timestamp>". That is followed by the LBAs in hex (and prefixed with "0x") of any block that cannot be read, one LBA per line. If the sense data does not correctly identify the LBA of the first error in the range it was asked to read then a LBA range is reported in the form of the lowest and the highest LBA in the range separated by a "-". At the end of the copy a line with "# stop <timestamp>" is appended to "errblk.txt". Typically used with "coe".

excl [io] [reg,blk]

causes the O_EXCL flag to be added to the open of IFILE and/or OFILE. See open(2) man page.

fdatasync [o] [reg,blk]

Flushes data associated with the OFILE to storage at the end of the copy.

flock [io] [reg,blk,pt]

after opening the associated file (i.e. IFILE and/or OFILE) an attempt is made to get an advisory exclusive lock with the flock() system call. The flock arguments are "FLOCK_EX | FLOCK_NB" which will cause the lock to be taken if available else a "temporarily unavailable" error is generated. An exit status of 90 is produced in the latter case and no copy is done. See flock(2) man page.

force [io] [pt] [xcopy,odx]

override difference between given block size and the block size found by the SCSI READ CAPACITY command. Use the given block size. Without this flag the copy would not be performed. pt access to what appears to be a block partition is aborted in version 0.92; that can be overridden by the force flag. For related reasons the 'norcap' flag requires this flag when applied to a block device accessed via pt.
xcopy and odx: various limits imposed by associated VPD pages or the RECEIVE COPY OPERATING PARAMETERS command can be overridden (i.e. exceeded) if this flag is given. Note that the copy manager will probably object.

fsync [o] [reg,blk]

Flushes data and metadata (describing the file) associated with the OFILE to storage at the end of the copy.

fua [io] [pt]

causes the FUA (force unit access) bit to be set in SCSI READ and/or WRITE commands. The 6 byte variants of the SCSI READ and WRITE commands do not support the FUA bit.

fua_nv [io] [pt]

causes the FUA_NV (force unit access non-volatile cache) bit to be set in SCSI READ and/or WRITE commands. This only has an effect with pt devices. The 6 byte variants of the SCSI READ and WRITE commands do not support the FUA_NV bit. The FUA_NV bit was made obsolete in SBC-3 revision 35d.

ignoreew [o] [tape]

ignore the early warning indication (of end of tape) when writing to tape. See TAPE section.

immed [io] [odx]

sets the IMMED bit in the POPULATE TOKEN (when [i]) or WRITE USING TOKEN (when [o]) command. That command should return status promptly after starting the data transfer. The RECEIVE ROD TOKEN INFORMATION command is then used to poll for completion. SCSI command timeouts should not be exceeded, even for very large RODs, if this flag is used.

nocache [io] [reg,blk]

use posix_fadvise(POSIX_FADV_DONTNEED) to advise corresponding file there is no need to fill the file buffer with recently read or written blocks. If used with "iflag=" it will increase the read ahead on IFILE.

no_del_tkn [o] [odx]

will clear the DEL_TKN bit on the last WRITE USING TOKEN command of each ROD Token in a odx full copy. In a large odx full copy several ROD Tokens may be used (one after the other). The default action is to set the DEL_TKN bit on the last WUT command of each ROD. Either way it should not make much difference because the copy manager deletes a ROD Token after a copy is completed. The copy manager will also delete/invalidate a ROD Token if the inactivity timeout is reached.

nofm [o] [tape]

no File Mark (FM) on close when writing to tape. See TAPE section.

nopad [o] [tape]

when the block to be written to a tape drive contains less than OBS bytes, then this option causes the partial block to be written as is. The default action for a tape in this case is to pad the block. See TAPE section.

norcap [io] [pt]

do not perform SCSI READ CAPACITY command on the corresponding pt device. If used on block device accessed via pt then 'force' flag is also required. This is to warn about using pt access on what may be a block device partition.

nowrite [o] [reg,blk,pt]

bypass writes to OFILE. The "records out" count is not incremented. OFILE is still opened but "oflag=trunc" if given is ignored. Also the ftruncate call associated with the sparse flag is ignored (i.e. bypassed). Commands such as trim and SCSI SYNCHRONIZE CACHE are still sent.

null [io]

has no affect, just a placeholder.

odx [io] [odx]

indicates to this utility that one of the four variants of an odx copy is requested. Using any of the --odx, rtf=RTF or rtype=RTYPE options also indicates that odx is requested. See the ODX section.

pad [o] [reg,blk,pt], [io] [xcopy]

when the block to be written (typically the last block) contains less than OBS bytes, then this option causes the block to be padded with zeros (i.e. bytes of binary zero). The default action for a regular file and a fifo is to do a partial write. The default action of a block and a pt device is to ignore the partial write. The default action of a tape is to pad, so this flag is not needed (see the nopad flag).
xcopy: sets the PAD bit in the CSCD descriptor of the associated IFILE or OFILE. Is associated with residual data handling and works together with the cat flag. See the XCOPY section below.

prealloc [o] [reg]

use the fallocate() call prior to starting a copy to set OFILE to its expected size.

pt [io] [blk,pt]

causes a device to be accessed in "pt" mode. In "pt" mode SCSI READ and WRITE commands are sent to access blocks rather than standard UNIX read() and write() commands. The "pt" mode may be implicit if the device is only capable of passing through SCSI commands (e.g. the /dev/sg* and some /dev/bsg/* devices in Linux). This flag is needed for device nodes that can be accessed both via standard UNIX read() and write() commands as well as SCSI commands. Such devices default standard UNIX read() and write() commands in the absence of this flag.

rarc [i] [pt]

bit set in READ(10, 12, 16 and 32) to suppress RAID rebuild functions when a bad (or recovered after difficulties) block is detected.

resume [o] [reg]

when a copy is interrupted (e.g. with Control-C from the keyboard) then using the same invocation again with the addition of "oflag=resume" will attempt to restart the copy from the point of the interrupt (or just before that point). It is harmless to use "oflag=resume" when OFILE doesn't exist or is zero length. If the length of OFILE is greater than or equal to the length implied by a ddpt invocation that includes "oflag=resume" then no further data is copied.

self [io] [pt]

used together with trim flag to do a self trim (trim of segments of a pt device that contain all zeros). If OFILE is not given, then it is set to the same as IFILE. If SEEK is not given it set to the same value as SKIP (possibly adjusted if IBS and OBS are different). Implicitly sets "nowrite" flag.

sparing [o] [reg,blk,pt]

during the copy each IBS * BPT byte segment is read from IFILE into a buffer. Then, instead of writing that buffer to OFILE, the corresponding segment is read from OFILE into another buffer. If the two buffers are different, the former buffer is written to the OFILE. If the two buffers compare equal then the write to OFILE is not performed. Write sparing is useful when a write operation is significantly slower than a read. Under some conditions flash memory devices have slow writes plus an upper limit on the number of times the same cell can be rewritten. The granularity of the comparison can be reduced from the default IBS * BPT byte segment with the the OBPC value given to the "bpt=" option. The finest granularity is when OBPC is 1 which implies OBS bytes.

sparse [o] [reg,blk,pt]

after each IBS * BPT byte segment is read from IFILE, it is checked to see if it is all zeros. If so, that segment is not written to OFILE. See the section on SPARSE WRITES below. The granularity of the zero comparison can be reduced from the default IBS * BPT byte segment with the OBPC value given to the "bpt=" option.

ssync [o] [pt]

if OFILE is in "pt" mode then the SCSI SYNCHRONIZE CACHE command is sent to OFILE at the end of the copy.

strunc [o] [reg]

perform a sparse copy with a ftruncate system call to extend the length of the OFILE if required. See the sparse flag and the section on SPARSE WRITES below.

sync [io] [reg,blk]

causes the O_SYNC flag to be added to the open of IFILE and/or OFILE. See open(2) man page.

rtf_len [io] [odx]

odx: with the 'read to tokens' variant, after 512 bytes of each ROD Token are written to IRTF an additional 8 byte (big endian) integer is written. That integer is the number of bytes the associated ROD represents. The draft standards say for standard ROD types the ROD Token holds this value. However vendor specific ROD types may be used or the vendors may choose not to comply. Either way the 'write from tokens' variant needs to know the size of the ROD it is writing from.

trim [io] [pt] [experimental]

similar logic to the "sparse" option. However instead of skipping segments that are full of zeros a "trim" command is sent to OFILE. Usually set as an oflag argument but for self trim can be used as an iflag argument (e.g. "iflag=self,trim"). Depending on the usage this may require the device to support "deterministic read zero after trim". See the TRIM, UNMAP AND WRITE SAME section below.

trunc [o] [reg]

if OFILE is a regular file then it is truncated prior to starting the copy. If SEEK is not given or 0 then OFILE is truncated to zero length; when SEEK is larger than zero the truncation takes place at file byte pointer SEEK*OBS. Ignored if "oflag=append". Conflicts with "oflag=sparing".

unmap [io] [pt]

same as the trim flag.

xcopy [io] [pt]

invoke SCSI XCOPY(LID1) logic and send the XCOPY command to the either IFILE or OFILE depending on which flag this called. If both are given (i.e. an invocation including 'iflag=xcopy oflag=xcopy') then send the XCOPY(LID1) to OFILE.

XCOPY

This section describes XCOPY(LID1) support with this utility. For ODX support (XCOPY(LID4) subset) see the ODX section.

A device (logical unit (LU)) that supports XCOPY operations should set the 3PC field (3PC stands for Third Party Copy) in its standard INQUIRY response. That is not checked when this utility does an xcopy operation but if it fails, that is one thing that the user may want to check.

If the xcopy starts and fails while underway, then 'sg_copy_results -s' may be useful to view the copy status. It might also be used from a different process with the same I_T nexus (i.e. the same machine) to check status during an xcopy operation.

The pad and cat flags control the handling of residual data. As the data can be specified either in terms of source or target block size and both might have different block sizes residual data is likely to happen in these cases. If both block sizes are identical these bits have no effect as residual data will not occur.

If neither of these flags are set, the EXTENDED COPY command will be aborted with additional sense 'UNEXPECTED INEXACT SEGMENT'.

If only the cat flag is set the residual data will be retained and made available for subsequent segment descriptors. Residual data will be discarded for the last segment descriptor.

If the pad flag is set for the source descriptor only, any residual data for both source or destination will be discarded.

If the pad flag is set for the target descriptor only any residual source data will be handled as if the cat flag is set, but any residual destination data will be padded to make a whole block transfer.

If the pad flag is set for both source and target any residual source data will be discarded, and any residual destination data will be padded.

There is a web page discussing ddpt, XCOPY and ODX at http://sg.danny.cz/sg/ddpt_xcopy_odx.html

ODX

This section describes ODX support (an XCOPY(LID4) subset) for this utility. ODX descriptions use the following command name abbreviations: PT for the POPULATE TOKEN command, RRTI for the READ ROD TOKEN INFORMATION command, and WUT for the WRITE USING TOKEN command.

A device (logical unit (LU)) that supports ODX operations is required to set the 3PC field (3PC stands for Third Party Copy) in its standard INQUIRY response and support the Third Party Copy VPD page. If this utility generates errors noting the absence of these then the device in question probably does not support ODX.

There a four variants of ODX supported by ddpt:

  full copy : ddpt --odx if=/dev/sg3 bs=512 of=/dev/sg4

  zero output blocks : ddpt if=/dev/null rtype=zero bs=512 of=/dev/sg4

  read to tokens : ddpt if=/dev/sg3 bs=512 [email protected] rtf=a.rt

  write from tokens : ddpt rtf=a.rt bs=512 of=/dev/sg4 [email protected]

The full copy will call PT and WUT commands repeatedly until the copy is complete. More precisely the full copy will make the largest single call to PT allowed by the input's Third Party Copy VPD page (and, if given, allowed by the BPT argument in the bpt=BPT[,OBPC] option). Then one or more WUT calls are made to write out from the ROD created by the PT step. The largest single WUT call is constrained by the output's Third Party Copy VPD page (and, if given, allowed by the OBPC argument in the bpt=BPT[,OBPC] option). This sequence continues until the requested copy is complete.

The zero output blocks variant is a special case of the full copy in which only WUT calls are made. ODX defines a special ROD Token to zero blocks. That special ROD Token has a fixed pattern (shown in SBC-3) and does not need to be created by a PT command like normal ROD Tokens.

The read to tokens and the write from tokens variants are designed to be the read (input) and write (output) sides respectively of a network copy. Each can run on different machines by sending the RTF file from the machine doing the read to the machine doing the write. The read to tokens will make one or more PT calls and output the resulting ROD Tokens to the RTF file. RTF might be a regular file or a named pipe.

All four variants can have the immed flag set. Then the PT and/or WUT commands are issued with the IMMED bit set and the RRTI command is used to poll for completion. The delay between the polls is as suggested by the RRTI command (or if no suggestion is made, 500 milliseconds). Either iflag=immed, oflag=immed or both can be given but are only effective if the corresponding IFILE or OFILE sends a PT or WUT command.

Typically there is no need to give the list_id=LID option. If this option is not given then 257 is chosen. If that is busy then 258 is tried. That continues until a usable LID is found or 10 LIDs have been tried. In the latter case ddpt exits with status of 55 (operation in progress). If the user gives list_id=LID option and LID is busy then ddpt exits with exit status 55.

If the block size of the input and output are different (i.e. IBS is not equal to OBS) then one must be a multiple of the other. So an input block size of 512 bytes and an output block size of 4096 bytes (or vice versa) is acceptable.

The four ODX variants are distinguished as follows: if OFILE is a pass-through device, if=/dev/null (or equivalent) and rtype=zero then the zero output blocks variant is selected. If both IFILE and OFILE are pass-through devices and there is some indication of an ODX request (e.g. the --odx option), then the full copy variant is selected. The read to tokens and the write from token variants are indicated by the absence of either a of=OFILE or a if=IFILE option, respectively, plus the presence of a rtf=RTF option.

The helper utility ddptctl contains options to issue a single PT, RRTI, WUT or COPY OPERATION ABORT command. It can also issue a series of polling RRTI commands. It can decode information in ROD Tokens (which is not as informative as it should be) and print the number of blocks and block size of a disk, plus protection information if available. See ddptctl.

There is a web page discussing ddpt, XCOPY and ODX at http://sg.danny.cz/sg/ddpt_xcopy_odx.html

SPARSE WRITES

Bypassing writes of blocks full of zeros can save a lot of IO. However with regular files, bypassed writes at the end of the copy can lead to an OFILE which is shorter than it would have been without sparse writes. This can lead to integrity checking programs like md5sum and sha1sum generating different values.

This utility has two ways of handling this file length problem: writing the last block (even if it is full of zeros) or using the ftruncate system call. A third approach is to ignore the problem (i.e. leaving OFILE shorter). The ftruncate approach is used when "oflag=strunc" while the last block is written when "oflag=sparse". To ignore the file length issue use "oflag=sparse,sparse". Note that if OFILE's length is already correct or longer than required, no action is taken.

The support for sparse writing of regular files may depend on the OS, the file system and the settings of OFILE. POSIX makes few guarantees when the ftruncate system call is used to extend a file's length, as may occur when "oflag=strunc". Further, primitive file systems like VFAT may not accept sparse writes or simulate the effect by writing blocks of zeros. The latter approach will defeat any sparse writing performance gain.

TRIM, UNMAP AND WRITE SAME

This is a new storage feature often associated with Solid State Disks (SSDs) or disk arrays with "thin provisioning". In the ATA command set (ACS-2) the relevant command is DATA SET MANAGEMENT with the TRIM bit set. In the SCSI command set (SBC-3) it is either the UNMAP or WRITE SAME command. Note there is no TRIM command however the term is frequently used in the technical press.

Trim is a way of telling a storage device that blocks are no longer needed. Keeping the pool of unwritten blocks large is important for the write performance of SSDs and the thrifty use of real storage in thin provisioned arrays. Currently file systems in recent OSes may issue trims associated with file deletes. The trim option in ddpt may be useful when a partition or a whole SSD is to be "deleted". Note that ddpt is bypassing file systems in that it only offers trim on pass-through (pt) devices.

This utility issues SCSI commands to pt devices and for "trim" currently issues a SCSI WRITE SAME(16) command with the UNMAP bit set. If the pt device is a SSD with a ATA interface then recent versions of Linux will translate the SCSI WRITE SAME to the ATA DATA SET MANAGEMENT command with the TRIM bit set. The maximum size of each "trim" command sent is the size of the copy buffer (i.e. IBS * BPT bytes). And that maximum can be reduced with the OBPC argument of the "bpt=" option.

The trim can be used various ways. One way is a copy where the copy buffer (or some part of it) is checked for zeros as is done by the sparse oflag. When a zero segment is found, a trim "command" is sent to the OFILE. For example:

   ddpt if=dsk.img bs=512 of=/dev/sdc oflag=pt,trim

The copy buffer is 64 KiB (since BPT and OBPC default to 128 when "bs=512") and it is checked for all zeros. If it is all zeros then a trim command is sent to the corresponding location of /dev/sdc which is accessed via the pt interface. If it is not all zeros then a SCSI WRITE command is sent. Another way is to trim all or part of a disk. To trim a whole disk (i.e. deleting all its data):

   ddpt if=/dev/zero bs=512 of=/dev/sdc oflag=pt,trim

A third way is to "self-trim" which is to only trim those parts of a disk that contain segments full of zeros:

   ddpt if=/dev/sdc skip=0x2300 bs=512 iflag=pt,self,trim count=0x1234f0

The "self" oflag automatically sets up the output side of the copy to send trim commands (if required) back the the same device (i.e. /dev/sdc). If this example was self-trimming a partition then the partition would start at LBA 0x2300 and be 0x1234f0 blocks long.

Some random product examples: the Intel X25-M G2 SSDs have trim with recent firmware and they do deterministic read zero after trim. The Seagate Pulsar SSD has an ATA interface which supports the deterministic reads of zero after the DATA SET MANAGEMENT command with the TRIM option.

DD DIFFERENCES

dd defaults "if=" and "of=" to stdin and stdout respectively. This follows Unix filter conventions. However since dd and ddpt are often used to read binary data for timing purposes, having to supply "of=/dev/null" can be easily forgotten. Without it dd will typically spew binary data on the console. So ddpt has changed its defaults: the "if=IFILE" is now mandatory for direct copies and to read from stdin "if=-" can be used; "of=OFILE" remains optional but its default changes to "/dev/null" (or "NUL" in Windows). To send output to stdout ddpt accepts "of=-".

dd truncates OFILE unless "conv=notrunc" is given. When dd truncates, it truncates to zero length unless SEEK is greater than zero. ddpt does not truncate OFILE by default. If OFILE exists it will be overwritten. The overwrite starts at block zero unless SEEK or "oflag=append" is given. If OFILE is a regular file then "oflag=trunc" (or "conv=trunc") will truncate OFILE prior to the copy.

Numeric arguments to ddpt can be given in hexadecimal, either with a leading "0x" or "0X" or with a trailing "h". Note that dd accepts "0x123" but interprets it as "0 * 123" (i.e. zero). ddpt will also interpret "x" as multiplies unless the left operand is zero (e.g. "0x123"). So both dd and ddpt will interpret "skip=2x123" as "skip=246".

Terabyte size disks make it impractical to copy all the data into a buffer before writing it out. Therefore both dd and ddpt read a relatively small amount of data into a copy (or transfer) buffer then write it out to the destination, repeating this process until the COUNT is exhausted.

A major difference in ddpt is the addition of BPT to control the size of the copy buffer. With dd, IBS is the size of the copy buffer and the unit of SKIP and COUNT. With ddpt, IBS * BPT is the size of the copy buffer and IBS is the unit of SKIP and COUNT. This allows ddpt to have its IBS set to the logical block size of IFILE without unduly restricting the size of the copy buffer. And setting IBS (and OBS for OFILE) accurately is required when the pass-through interface is used since with the SCSI READ and WRITE commands the logical block size is implicit.

The way dd handles its copy buffer (outlined in SUSv4 description of dd) is relatively complex, especially when IBS and OBS are different sizes. The restriction that ddpt places on IBS and OBS ( i.e. (((IBS * BPT) % OBS) == 0) ) means that a single copy buffer can be used since its size is a multiple of both IBS and OBS. Being able to precisely define the copy buffer size in ddpt makes sparse writing, write sparing and trim operations simpler to define and the user to control.

ddpt does not support dd's "cbs=" option (conversion block size). If the "cbs=" option is given to ddpt then it is ignored.

ddpt adds two types of disk to disk, offloaded copies: XCOPY(LID1) first introduced in SPC-2 (standardized in 2001), and ODX which is a subset of XCOPY(LID4) first introduced in SPC-4 draft (revision 34, 2012).

PROTECTION INFORMATION

This section is about protection information which is typically an extra 8 bytes associated with each logical block. Those 8 byte are divided into 3 fields: logical block guard (16 bit (2 byte) CRC), logical block application tag (2 bytes) and the logical block reference tag (4 bytes). The acronym DIF is sometimes used for protection information.

The feature to read and/or write protection information by using the protect=RDP[,WRP] option is currently experimental. It should be used with care and may not "play well" with some other features such as write sparing and sparse writing. It should be used to copy user data plus the associated protection information to or from a regular file. It could also be used for a device to device copy assuming the "pt" interface is used for both. Also only modern SCSI disks support protection information.

When RDP or WRP is greater than 0 then a copy with associated protection information is active. In this state IBS and OBS must be the same and equal to the logical block size of the device(s) formatted with protection information. If a SCSI disk with 512 byte logical block size has protection information then the actual number of bytes transferred for each logical block is typically 520 bytes. For such a disk BS=512 is required even when additional protection information is being transferred.

MULTIPLIERS

By default numeric arguments to options are assumed to be decimal. Almost all numeric arguments to options (e.g. COUNT in the count=COUNT option) may include one of these multiplicative suffixes: c C *1; w W *2; b B *512; k K KiB *1,024; KB *1,000; m M MiB *1,048,576; MB *1,000,000 . This pattern continues for "G", "T" and "P". The latter two suffixes can only be used for 64 bit values. Some numeric arguments are limited to 32 bit values (e.g. BSin the bs=BS option). Also a suffix of the form "x<n>" multiplies the leading number by <n>; however the combinations "0x" and "0X" are treated differently, see the next paragraph. These multiplicative suffixes are compatible with GNU's dd command (since 2002) which claims compliance with the SI and with IEC 60027-2 standards.

Alternatively numerical values can be given in hexadecimal indicated by either a leading "0x" or "0X", or by a trailing "h" or "H". When hex numbers are given, suffix multipliers cannot be used.

If a numeric argument is required to fit in 32 bits and is too large then an error is reported. Usually negative numbers are not permitted but "count=-1" is a special case and means "all available"; "verbose=-1" is another special case.

NOTES

A partial write is a write to the OFILE of less than OBS bytes. This typically occurs at the end of a copy. dd can do partial writes. ddpt does partial writes to regular files and fifos (including stdout). However ddpt ignores partial writes when OFILE is a block device or a pt device. When ddpt ignores a partial write, it sends a warning to the console (stderr).

At the end of the copy two lines are reported to the console:

   <in_full>+<in_partial> records in

   <out_full>+<out_partial> records out

The "records in" line is the number of full input blocks (each of IBS bytes) that have been read plus the number of partial blocks ( usually less than IBS bytes) that have been read. Following the lead of dd when 'iflag=coe' is active a block that cannot be read (and has zeros substituted for its output) is regarded as a partial read. The "records out" line is the number of full output blocks (each of OBS bytes) that have been written plus the number of partial blocks (usually less than OBS bytes) that have been written.

Block devices (e.g. /dev/sda and /dev/hda) can be given for IFILE. If neither 'iflag=direct' nor 'iflag=pt' is given then normal block IO involving buffering and caching is performed. If 'iflag=direct' is given then the buffering and caching is bypassed (this is applicable to both SCSI devices and ATA disks). When 'iflag=pt' is given SCSI commands are sent to the device which bypasses most of the actions performed by the block layer. The same applies for block devices given for OFILE.

All informative, warning and error reports are sent to stderr so that dd's output file can be stdout and remain unpolluted. If no options are given, then no copying (nor reading) takes place and a brief message is sent to stderr inviting the user to invoke ddpt again but with '--help' option to get the usage message.

Disk partition information can often be found with fdisk(8) [the "-ul" argument is useful in this respect]. Also parted(8) can be used like this: 'parted /dev/sda unit s print' .

For pt devices this utility issues SCSI READ and WRITE (SBC) commands which are appropriate for disks and reading from CD/DVD/BD drives. Those commands are not formatted correctly for tape drives so ddpt cannot be used on tape drives via a pt device. If the largest block address of the requested transfer exceeds a 32 bit block number (i.e 0xffffffff) then a warning is issued and the pt device is accessed via SCSI READ(16) and WRITE(16) commands.

The attributes of a block device (e.g. partitions) are ignored when the pt flag is used. Hence the whole device is read (rather than just the second partition) by this invocation:

   ddpt if=/dev/sdb2 iflag=pt of=t bs=512

Assuming /dev/sdb and /dev/sg2 refer to the same device, then after the following two invocations, the contents of the files "t", "tt" and "ttt" should be same:

   ddpt if=/dev/sdb of=tt bs=512

   ddpt if=/dev/sg2 of=ttt bs=512

The SCSI READ(32) and WRITE(32) commands are restricted to media that is formatted with protection type 2. This is a T10 restriction.

TAPE

There is support for copies to and from tape drives in Linux. Only the st driver device names can be used (e.g. /dev/st0 and /dev/nst2). Hence use of Linux pass-through device names (e.g. /dev/sg2) for tape drives is not supported. On Debian-based distributions, it is suggested that the mt-st package is installed as it provides a more fully-featured version of the "mt" tape control program.

Tape drives can operate in fixed- or variable-length block modes. In variable-block mode, each write to the tape writes a single block of that size. In fixed-block mode, each write to the tape must be a multiple of the previously-selected block size.

The block size/mode can be set with the mt command prior to invoking ddpt. For example:

  # mt -f /dev/nst0 setblk 0
sets variable-block mode, and

  # mt -f /dev/nst0 setblk 32768
sets fixed-block mode with block size 32768 bytes.

Note that some tape drives support only fixed-block mode, and possibly even only one block size. (For example, QIC-150 tapes use a fixed block size of 512 bytes.) There may also be restrictions on the block size, e.g. it may have to be even.

When using ddpt to write to tape, if the final read from the input is less than OBS, it is padded to OBS bytes before writing to tape to ensure that all blocks of the tape file are the same length. Having a shorter final block would fail if the drive is in fixed-block mode, and could create interchange problems. It is common to expect all blocks in a file on tape to be the same length. However, to tell ddpt to not pad the final block, use 'oflag=nopad'.

The st tape driver normally writes a filemark when the file (e.g. /dev/nst0) is closed. To not have the filemark written, use 'oflag=nofm'. One use case for that might be if using ddpt several times in succession to append more data to the same file on tape. In that case it is probably desirable to write the filemark at the end of the sequence. So either omit 'oflag=nofm' on the last ddpt invocation, or manually write a filemark using mt after ddpt exits:

  # mt -f /dev/nst0 weof 1

For reading from an unknown tape where the block size(s) is not known, read in variable-block mode specifying a large IBS. The st driver returns a smaller amount of data if the size of the block read is smaller. Thus a command like:

  # ddpt if=/dev/nst0 of=output.bin bs=262144
should read the file from tape regardless of the block size used (assuming no blocks are larger than 256KB). ddpt's verbose option will display what the actual block size(s) is.

EXAMPLES

The examples in this page use Linux device names. For suitable device names in other supported Operating Systems see this web page: http://sg.danny.cz/sg/device_name.html . The sg3_utils(8) man page in the sg3_utils package also covers device naming.

ddpt usage looks quite similar to dd:

   ddpt if=/dev/sg0 of=t bs=512 count=1MB

This will copy 1 million 512 byte blocks from the device associated with /dev/sg0 (which should have 512 byte blocks) to a file called t. Assuming /dev/sda and /dev/sg0 are the same device then the above is equivalent to:

   dd if=/dev/sda iflag=direct of=t bs=512 count=1000000

although dd's speed may improve if bs was larger and count was suitably reduced. The use of the 'iflag=direct' option bypasses the buffering and caching that is usually done on a block device.

The dd command's bs argument can be thought of as roughly equivalent to ddpt's bs*bpt . dd almost assumes buffering on a block device and will work as long as bs is a multiple of the actual logical block size. Since ddpt can work at a lower level in some cases the bs argument must be a disk's actual logical block size. Thus the bpt argument was introduced to make the copy more efficient. So these two invocations are roughly equivalent:

   dd if=/dev/sda of=t bs=8k count=64

   ddpt if=/dev/sda of=t bs=512 bpt=16 count=1k

In both cases the total number of bytes moved is bs*count . And that will be done by reading 8k (8192 bytes) into a buffer then writing out that buffer to the file t. The read write sequence continues until the count is complete or an error occurs.

The 'of2=' option can save time when the input would otherwise need to be read twice. For example, to copy data and take a md5sum of it without needing to re-read the data:

  mkfifo fif

  md5sum fif &

  ddpt if=/dev/sg3 iflag=coe of=sg3.img oflag=sparse of2=fif bs=512

This will image /dev/sg3 (e.g. an unmounted disk) and place the contents in the (sparse) file sg3.img . Without re-reading the data it will also perform a md5sum calculation on the image.

Now we use sparse writing logic to get some idea of how many blocks on a disk are full of zeros. After a SCSI FORMAT UNIT command or an ATA SECURITY ERASE command a disk may be all zeros.

   ddpt if=/dev/sdc bs=512 oflag=sparse

Since no "of=" option is given, output goes to /dev/null so nothing is actually written so the "records out" will be zero. However there will be a count of "records in" and "bypassed records out". If /dev/sdc is full of zeros then "records in" and "bypassed records out" will be the same. Since the "bpt=" option is not given it defaults to "bpt=128,128" so the copy buffer will be 64 KiB and the sparse check for zeros will be done with 64 KiB (128 block) granularity.

For examples of the trim and self,trim options see the section above on TRIM, UNMAP AND WRITE SAME.

Following is an example run on a Windows OS using the '--wscan' option which shows the available device names (e.g. PD1) and the associated volume name(s):

   ddpt -w
PD0 [C] FUJITSU MHY2160BH 0000
PD1 [DF] WD 2500BEV External 1.05 WD-WXE90
CDROM0 [E] MATSHITA DVD/CDRW UJDA775 CB03

So, for example, volumes D: and F: reside on PhysicalDisk1 (abbreviated to "PD1") which is manufactured by WD (Western Digital).

Further examples can be found on this web page: http://sg.danny.cz/sg/ddpt.html . There is a text file containing examples called ddpt_examples.txt in the "doc" directory of this package's distribution tarball.

AUTHORS

Written by Doug Gilbert

REPORTING BUGS

Report bugs to <dgilbert at interlog dot com>.

COPYRIGHT

Copyright © 2008-2014 Douglas Gilbert
This software is distributed under the GPL version 2. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.