# man > sgp_dd(8) [SGP_DD(8)](https://www.chedong.com/phpMan.php/man/SGPDD/8/markdown) SG3_UTILS [SGP_DD(8)](https://www.chedong.com/phpMan.php/man/SGPDD/8/markdown) ## NAME sgp_dd - copy data to and from files and devices, especially SCSI devices ## SYNOPSIS **sgp**___**dd** [_bs=BS_] [_count=COUNT_] [_ibs=BS_] [_if=IFILE_] [_iflag=FLAGS_] [_obs=BS_] [_of=OFILE_] [_oflag=FLAGS_] [_seek=SEEK_] [_skip=SKIP_] [_--help_] [_--version_] [_bpt=BPT_] [_coe=_0|1] [_cdbsz=_6|10|12|16] [_deb=VERB_] [_dio=_0|1] [_sync=_0|1] [_thr=THR_] [_time=_0|1] [_verbose=VERB_] [_--dry-run_] [_--verbose_] ## DESCRIPTION Copy data to and from any files. Specialised for "files" that are Linux SCSI generic (sg) and raw devices. Similar syntax and semantics to [**dd(1)](https://www.chedong.com/phpMan.php/man/dd/1/markdown)** but does not perform any conversions. Uses POSIX threads (often called "pthreads") to increase the amount of parallelism. This improves speed in some cases. The first group in the synopsis above are "standard" Unix [**dd(1)](https://www.chedong.com/phpMan.php/man/dd/1/markdown)** operands. The second group are extra options added by this utility. Both groups are defined below. ## OPTIONS **bpt**=_BPT_ each IO transaction will be made using _BPT_ blocks (or less if near the end of the copy). Default is 128 for block sizes less that 2048 bytes, otherwise the default is 32. So for bs=512 the reads and writes will each convey 64 KiB of data by default (less if near the end of the transfer or memory restrictions). When cd/dvd drives are accessed, the block size is typically 2048 bytes and bpt defaults to 32 which again implies 64 KiB transfers. **bs**=_BS_ where _BS_ **must** be the block size of the physical device. Note that this differs from [**dd(1)](https://www.chedong.com/phpMan.php/man/dd/1/markdown)** which permits 'bs' to be an integral multiple of the actual device block size. Default is 512 which is usually correct for disks but incorrect for cdroms (which nor‐ mally have 2048 byte blocks). **cdbsz**=6 | 10 | 12 | 16 size of SCSI READ and/or WRITE commands issued on sg device names. Default is 10 byte SCSI command blocks (unless calculations indicate that a 4 byte block number may be exceeded, in which case it defaults to 16 byte SCSI commands). **coe**=0 | 1 set to 1 for continue on error. Only applies to errors on sg devices. Thus errors on other files will stop sgp_dd. Default is 0 which implies stop on any error. See the 'coe' flag for more information. **count**=_COUNT_ copy _COUNT_ blocks from _IFILE_ to _OFILE_. Default is the minimum (of _IFILE_ and _OFILE_) number of blocks that sg devices report from SCSI READ CAPACITY commands or that block devices (or their partitions) report. Normal files are not probed for their size. If _skip=SKIP_ or _seek=SEEK_ are given and the count is deduced (i.e. not explicitly given) then that count is scaled back so that the copy will not overrun the device. If the file name is a block device partition and _COUNT_ is not given then the size of the par‐ tition rather than the size of the whole device is used. If _COUNT_ is not given and cannot be deduced then an error message is issued and no copy takes place. **deb**=_VERB_ outputs debug information. If _VERB_ is 0 (default) then there is minimal debug informa‐ tion and as _VERB_ increases so does the amount of debug (max debug output when _VERB_ is 9). **dio**=0 | 1 default is 0 which selects indirect IO. Value of 1 attempts direct IO which, if not available, falls back to indirect IO and notes this at completion. If direct IO is se‐ lected and /proc/scsi/sg/allow_dio has the value of 0 then a warning is issued (and indirect IO is performed) For finer grain control use 'iflag=dio' or 'oflag=dio'. **ibs**=_BS_ if given must be the same as _BS_ given to 'bs=' option. **if**=_IFILE_ read from _IFILE_ instead of stdin. If _IFILE_ is '-' then stdin is read. Starts reading at the beginning of _IFILE_ unless _SKIP_ is given. **iflag**=_FLAGS_ where _FLAGS_ is a comma separated list of one or more flags outlined below. These flags are associated with _IFILE_ and are ignored when _IFILE_ is stdin. **obs**=_BS_ if given must be the same as _BS_ given to 'bs=' option. **of**=_OFILE_ write to _OFILE_ instead of stdout. 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 (this is a shorthand notation). If _OFILE_ exists then it is _not_ truncated; it is overwritten from the start of _OFILE_ unless 'oflag=append' or _SEEK_ is given. **oflag**=_FLAGS_ where _FLAGS_ is a comma separated list of one or more flags outlined below. These flags are associated with _OFILE_ and are ignored when _OFILE_ is /dev/null, '.' (period), or stdout. **seek**=_SEEK_ start writing _SEEK_ bs-sized blocks from the start of _OFILE_. Default is block 0 (i.e. start of file). **skip**=_SKIP_ start reading _SKIP_ bs-sized blocks from the start of _IFILE_. Default is block 0 (i.e. start of file). **sync**=0 | 1 when 1, does SYNCHRONIZE CACHE command on _OFILE_ at the end of the transfer. Only ac‐ tive when _OFILE_ is a sg device file name. **thr**=_THR_ where _THR_ is the number or worker threads (default 4) that attempt to copy in paral‐ lel. Minimum is 1 and maximum is 1024. **time**=0 | 1 when 1, the transfer is timed and throughput calculation is performed, outputting the results (to stderr) at completion. When 0 (default) no timing is performed. **verbose**=_VERB_ increase verbosity. Same as _deb=VERB_. Added for compatibility with sg_dd and sgm_dd. ### -d --dry-run does all the command line parsing and preparation but bypasses the actual copy or read. That preparation may include opening _IFILE_ or _OFILE_ to determine their lengths. This option may be useful for testing the syntax of complex command line invocations in advance of executing them. ### -h --help outputs usage message and exits. ### -v --verbose when used once, this is equivalent to _verbose=1_. When used twice (e.g. "-vv") this is equivalent to _verbose=2_, etc. ### -V --version outputs version number information and exits. ## FLAGS Here is a list of flags and their meanings: append causes the O_APPEND flag to be added to the open of _OFILE_. For normal files this will lead to data appended to the end of any existing data. Cannot be used together with the _seek=SEEK_ option as they conflict. The default action of this utility is to over‐ write any existing data from the beginning of the file 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. coe continue on error. When given with 'iflag=', an error that is detected in a single SCSI command (typically 'bpt' blocks) is noted (by an error message sent to stderr), then zeros are substituted into the buffer for the corresponding write operation and the copy continues. Note that the **sg**___**dd** utility is more sophisticated in such error situations when 'iflag=coe'. When given with 'oflag=', any error reported by a SCSI WRITE command is reported to stderr and the copy continues (as if nothing went wrong). dio request the sg device node associated with this flag does direct IO. If direct IO is not available, falls back to indirect IO and notes this at completion. If direct IO is selected and /proc/scsi/sg/allow_dio has the value of 0 then a warning is issued (and indirect IO is performed). direct causes the O_DIRECT flag to be added to the open of _IFILE_ and/or _OFILE_. This flag re‐ quires some memory alignment on IO. Hence user memory buffers are aligned to the page size. Has no effect on sg, normal or raw files. dpo 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. dsync causes the O_SYNC flag to be added to the open of _IFILE_ and/or _OFILE_. The 'd' is prepended to lower confusion with the 'sync=0|1' option which has another action (i.e. a synchronisation to media at the end of the transfer). excl causes the O_EXCL flag to be added to the open of _IFILE_ and/or _OFILE_. mmap can only be used in the _iflag=FLAGS_ or the _oflag=FLAGS_ argument list but not both. The nominated side of the copy will use memory mapped IO based on the [mmap(2)](https://www.chedong.com/phpMan.php/man/mmap/2/markdown) system call. The sg driver will remap its DMA destination or source buffer into the user space when the [mmap(2)](https://www.chedong.com/phpMan.php/man/mmap/2/markdown) system call is used on a sg device. fua causes the FUA (force unit access) bit to be set in SCSI READ and/or WRITE commands. This only has effect with sg devices. The 6 byte variants of the SCSI READ and WRITE commands do not support the FUA bit. Only active for sg device file names. null has no affect, just a placeholder. ## RETIRED OPTIONS Here are some retired options that are still present: coe=0 | 1 continue on error is 0 (off) by default. When it is 1, it is equivalent to 'iflag=coe oflag=coe' described in the FLAGS section above. Similar to 'conv=noerror,sync' in [**dd(1)](https://www.chedong.com/phpMan.php/man/dd/1/markdown)** utility. Default is 0 which implies stop on error. More advanced coe=1 process‐ ing on reads is performed by the sg_dd utility. fua=0 | 1 | 2 | 3 force unit access bit. When 3, fua is set on both _IFILE_ and _OFILE_; when 2, fua is set on _IFILE_;, when 1, fua is set on _OFILE_; when 0 (default), fua is cleared on both. See the 'fua' flag. ## NOTES A raw device must be bound to a block device prior to using sgp_dd. See [**raw(8)](https://www.chedong.com/phpMan.php/man/raw/8/markdown)** for more in‐ formation about binding raw devices. To be safe, the sg device mapping to SCSI block devices should be checked with 'cat /proc/scsi/scsi' before use. Raw device partition information can often be found with [**fdisk(8)](https://www.chedong.com/phpMan.php/man/fdisk/8/markdown)** [the "-ul" argument is use‐ ful in this respect]. Various numeric arguments (e.g. _SKIP_) may include multiplicative suffixes or be given in hexadecimal. See the "NUMERIC ARGUMENTS" section in the [sg3_utils(8)](https://www.chedong.com/phpMan.php/man/sg3utils/8/markdown) man page. The _COUNT_, _SKIP_ and _SEEK_ arguments can take 64 bit values (i.e. very big numbers). Other val‐ ues are limited to what can fit in a signed 32 bit number. Data usually gets to the user space in a 2 stage process: first the SCSI adapter DMAs into kernel buffers and then the sg driver copies this data into user memory (write operations re‐ verse this sequence). This is called "indirect IO" and there is a 'dio' option to select "direct IO" which will DMA directly into user memory. Due to some issues "direct IO" is dis‐ abled in the sg driver and needs a configuration change to activate it. All informative, warning and error output is sent to stderr so that dd's output file can be stdout and remain unpolluted. If no options are given, then the usage message is output and nothing else happens. Why use sgp_dd? Because in some cases it is twice as fast as dd (mainly with sg devices, raw devices give some improvement). Another reason is that big copies fill the block device caches which has a negative impact on other machine activity. ## SIGNALS The signal handling has been borrowed from dd: SIGINT, SIGQUIT and SIGPIPE output the number of remaining blocks to be transferred and the records in + out counts; then they have their default action. SIGUSR1 causes the same information to be output yet the copy continues. All output caused by signals is sent to stderr. ## EXAMPLES Looks quite similar in usage to dd: sgp_dd 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 of=t bs=512 count=1000000 although dd's speed may improve if bs was larger and count was correspondingly scaled. Using a raw device to do something similar on a ATA disk: raw /dev/raw/raw1 /dev/hda sgp_dd if=/dev/raw/raw1 of=t bs=512 count=1MB To copy a SCSI disk partition to an ATA disk partition: raw /dev/raw/raw2 /dev/hda3 sgp_dd if=/dev/sg0 skip=10123456 of=/dev/raw/raw2 bs=512 This assumes a valid partition is found on the SCSI disk at the given skip block address (past the 5 GB point of that disk) and that the partition goes to the end of the SCSI disk. An explicit count is probably a safer option. To do a fast copy from one SCSI disk to another one with similar geometry (stepping over er‐ rors on the source disk): sgp_dd if=/dev/sg0 of=/dev/sg1 bs=512 coe=1 ## EXIT STATUS The exit status of sgp_dd is 0 when it is successful. Otherwise see the [sg3_utils(8)](https://www.chedong.com/phpMan.php/man/sg3utils/8/markdown) man page. Since this utility works at a higher level than individual commands, and there are 'coe' and 'retries' flags, individual SCSI command failures do not necessary cause the process to exit. ## AUTHORS Written by Douglas Gilbert and Peter Allworth. ## REPORTING BUGS Report bugs to . ## COPYRIGHT Copyright © 2000-2020 Douglas Gilbert This software is distributed under the GPL version 2. There is NO warranty; not even for MER‐ CHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. ## SEE ALSO A simpler, non-threaded version of this utility but with more advanced "continue on error" logic is called **sg**___**dd** and is also found in the sg3_utils package. The lmbench package con‐ tains **lmdd** which is also interesting. [**raw(8)](https://www.chedong.com/phpMan.php/man/raw/8/markdown),** [**dd(1)](https://www.chedong.com/phpMan.php/man/dd/1/markdown)** sg3_utils-1.45 February 2020 [SGP_DD(8)](https://www.chedong.com/phpMan.php/man/SGPDD/8/markdown)