sg_write_verify man page on DragonFly
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WRITE AND VERIFY(8) SG3_UTILS WRITE AND VERIFY(8)
NAME
sg_write_and_verify - send the SCSI WRITE AND VERIFY command
SYNOPSIS
sg_write_verify [--16] [--bytchk=BC] [--dpo] [--group=GN] [--help]
[--ilen=ILEN] [--in=IF] --lba=LBA [--num=NUM] [--repeat] [--timeout=TO]
[--verbose] [--version] [--wrprotect=WP] DEVICE
DESCRIPTION
Send a SCSI WRITE AND VERIFY (10) or (16) command to DEVICE. The data
to be written is read from the IF file or, in its absence, a buffer
full of 0xff bytes is used. The length of the data-out buffer sent with
the command is ILEN bytes or, if that is not given, then it is the
length of the IF file.
The write operation is to the DEVICE's medium (optionally to its cache)
starting at logical block address LBA for NUM logical blocks. After
the write to medium is performed a verify operation takes place which
may viewed as a medium read (with appropriate checks) but without the
data being returned. Additionally, if BS is set to one, the data read
back from the medium in the verify operation is compared to the origi‐
nal data-out buffer.
The relationship between the number of logical blocks to be written
(i.e. NUM) and the length (in bytes) of the data-out buffer (i.e.
ILEN) may be simply found by multiplying the former by the logical
block size. However if the DEVICE has protection information (PI) then
it becomes a bit more complicated. Hence the calculation is left to the
user with the default ILEN, in the absence of the IF file, being set to
NUM * 512.
For sending large amounts of data to contiguous logical blocks, a sin‐
gle WRITE AND VERIFY command may not be appropriate (e.g. due to oper‐
ating system limitations). In such cases see the REPEAT section below.
OPTIONS
Arguments to long options are mandatory for short options as well. The
options are arranged in alphabetical order based on the long option
name.
-S, --16
Send a WRITE AND VERIFY(16) command. The default is to send a
WRITE AND VERIFY(10) command unless LBA or NUM are too large for
the 10 byte variant.
-b, --bytchk=BC
where BC is the value to place in the command's BYTCHK field.
Values between 0 and 3 (inclusive) are accepted. The default is
value is 0 which implies only a write to the medium then a ver‐
ify operation are performed. The only other value T10 defines
currently is 1 which does performs an additional comparison
between the data-out buffer that was used by the write operation
and the contents of the logical blocks read back from the
medium.
-d, --dpo
Set the DPO (disable page out) bit in the command. The default
is to leave it clear.
-g, --group=GN
where GN is the value to place in the command's GROUP NUMBER
field. Values between 0 and 31 (inclusive) are accepted. The
default is value is 0.
-h, --help
output the usage message then exit.
-I, --ilen=ILEN
where ILEN is the number of bytes that will be placed in the
data-out buffer. If the IF file is given then no more than ILEN
bytes are read from that file. If the IF file does not contain
ILEN bytes then an error is reported. If the IF file is not
given then a data-out buffer with ILEN bytes of 0xff is sent.
-i, --in=IF
read data (binary) from file named IF. If IF is "-" then stdin
is used. This data will become the data-out buffer and will be
written to the DEVICE's medium. If BC is 1 then that data-out
buffer will be held until after the verify operation and com‐
pared to the data read back from the medium.
-l, --lba=LBA
where LBA is the logical block address to start the write to
medium. Assumed to be in decimal unless prefixed with '0x' or
has a trailing 'h'. Must be provided.
-n, --num=NUM
where NUM is the number of blocks, starting at LBA, to write to
the medium. The default value for NUM is 1.
-R, --repeat
this option will continue to do WRITE AND VERIFY commands until
the IF file is exhausted. This option requires both the
--ilen=ILEN and --in=IF options to be given. Each command starts
at the next logical block address and is for no more than NUM
blocks. The last command may be shorter with the number of
blocks scaled as required. If there are residue bytes a warning
is sent to stderr. See the REPEAT section.
-t, --timeout=TO
where TO is the command timeout value in seconds. The default
value is 60 seconds. If NUM is large then command may require
considerably more time than 60 seconds to complete.
-v, --verbose
increase the degree of verbosity (debug messages).
-V, --version
output version string then exit.
-w, --wrprotect=WP
set the WRPROTECT field in the cdb to WP. The default value is 0
which implies no protection information is sent (along with the
user data) in the data-out buffer.
REPEAT
For data sizes around a megabyte and larger, it may be appropriate to
send multiple SCSI WRITE AND VERIFY commands due to operating system
limitations (e.g. pass-through SCSI interfaces often limit the amount
of data that can be passed with a SCSI command). With this utility the
mechanism for doing that is the --repeat option.
In this mode the --ilen=ILEN and --in=IF options must be given. The
ILEN and NUM values are treated as a per SCSI command parameters. Up to
ILEN bytes will be read from the IF file continually until it is
exhausted. If the IF file is stdin, reading continues until an EOF is
detected. The data read from each iteration becomes the data-out buffer
for a new WRITE AND VERIFY command.
The last read from the file (or stdin) may read less than ILEN bytes in
which case the number of logical blocks sent to the last WRITE AND VER‐
IFY is scaled back accordingly. If there is a residual number of bytes
left after that scaling then that is reported to stderr.
If an error occurs then that is reported to stderr and via the exit
status and the utility stops at that point.
NOTES
Other SCSI WRITE commands have a Force Unit Access (FUA) bit but that
is set (implicitly) by WRITE AND VERIFY commands hence there is no
option to set it. The data-out buffer may still additionally be placed
in the DEVICE's cache and setting the DPO bit is a hint not to do that.
Normal SCSI WRITEs can be done with the ddpt and the sg_dd utilities.
The SCSI WRITE SAME command can be done with the sg_write_same utility
while the SCSI COMPARE AND WRITE command (sg_compare_and_write utility)
offers a "test and set" facility.
Various numeric arguments (e.g. LBA) may include multiplicative suf‐
fixes or be given in hexadecimal. See the "NUMERIC ARGUMENTS" section
in the sg3_utils(8) man page.
EXIT STATUS
The exit status of sg_write_verify is 0 when it is successful. If the
verify operation fails that is typically indicated with a medium error
which leads to an exit status of 3.
If BC is set to 1 and the comparison it causes fails this utility will
indicate the miscompare with an exit status of 14. For other exit sta‐
tus values see the EXIT STATUS section in the sg3_utils(8) man page.
EXAMPLES
To start with, a simple example: write 1 block of data held in file
t.bin that is 512 bytes long then write that block to LBA 0x1234 on
/dev/sg4 .
# sg_write_verify --lba=0x1234 --in=t.bin /dev/sg4
Since '--num=' is not given then it defaults to 1. Further the ILEN
value is obtained from the file size of t.bin . To additionally do a
data-out comparison to the read back data:
# sg_write_verify -l 0x1234 -i t.bin --bytchk=1 /dev/sg4
The ddpt command can do copies between SCSI devices using READ and
WRITE commands. However, currently it has no facility to promote those
WRITES to WRITE AND VERIFY commands. Using a pipe, that could be done
like this:
# ddpt if=/dev/sg2 bs=512 bpt=8 count=11 of=- |
sg_write_verify --in=- -l 0x567 -n 8 --ilen=4096 --repeat /dev/sg4
Both ddpt and sg_write_verify are configured for segments of 8 512 byte
logical blocks. Since 11 logical blocks are read then first 8 logical
blocks are copied followed by a copy of the remaining 3 blocks. Since
it is assumed that there is no protection information then the data-in
and data-out buffers will be 4096 bytes each. For sg_write_verify this
needs to be stated explicitly with the --ilen=4096 option.
AUTHORS
Bruno Goncalves and Douglas Gilbert.
REPORTING BUGS
Report bugs to <dgilbert at interlog dot com>.
COPYRIGHT
Copyright © 2014 Douglas Gilbert
This software is distributed under a FreeBSD license. There is NO war‐
ranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PUR‐
POSE.
SEE ALSO
ddpt(in a package of that name), sg_compare_and_write(8), sg_dd(8),
sg_write_same(8)
sg3_utils-1.40 July 2014 WRITE AND VERIFY(8)
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