sg_format - format or resize a SCSI disk (perhaps change its block
sg_format [--cmplst=0|1] [--count=COUNT] [--dcrt] [--early]
[--fmtpinfo=FPI] [--format] [--help] [--long] [--pfu=PFU] [--pie=PIE]
[--pinfo] [--resize] [--rto_req] [--security] [--six] [--size=SIZE]
[--verbose] [--version] [--wait] DEVICE
Not all SCSI direct access devices need to be formatted and some have
vendor specific formatting procedures. SCSI disks with rotating media
are probably the largest group that do support a ’standard’ format
operation. They are typically factory formatted to a block size of 512
bytes with the largest number of blocks that the manufacturer
recommends. The manufacturer’s recommendation typically leaves aside a
certain number of tracks, spread across the media, for reassignment of
logical block addresses during the life of the disk.
This utility can format modern SCSI disks and potentially change their
block size (if permitted) and the block count (i.e. number of
accessible blocks on the media also known as "resizing"). Resizing a
disk to less than the manufacturer’s recommended block count is
sometimes called "short stroking" (see NOTES section). Resizing the
block count while not changing the block size may not require a format
operation. The SBC-2 standard (see www.t10.org) has obsoleted the
"format device" mode page. Many of the low level details found in that
mode page are now left up to the discretion of the manufacturer.
When this utility is used without options (apart from a DEVICE) it
prints out the existing block size and block count derived from two
sources. These two sources are a block descriptor in the response to a
MODE SENSE command and the response to a READ CAPACITY command. The
reason for this double check is to detect a "format corrupt" state (see
NOTES section). This usage will not modify the disk.
When this utility is used with the "--format" (or "-F") option it will
attempt to format the given DEVICE. There is a 10 second pause during
which time the user is invited (twice 5 seconds apart) to abort
sg_format. This occurs just prior the SCSI FORMAT UNIT command being
issued. See the NOTES section for more information.
Recent SBC-3 drafts add several "protection types" to the "protection
information" introduced in the SBC-2 standard. See the "protection
information" section (section 4.18 in draft SBC-3 rev 18). 8 bytes of
protection information are added to each block (a 2 byte "logical block
guard" (CRC), a 2 byte "logical block application guard", and a 4 byte
"logical block reference tag"). A device that supports protection
information sets the "PROTECT" bit in its standard INQUIRY response.
The "FMTPINFO" field in in the FORMAT UNIT command cdb plus the
"Protection Field Usage" in the parameter header are associated with
protection information and can be set by this utility.
Arguments to long options are mandatory for short options as well. The
options are arranged in alphabetical order based on the long option
-C, --cmplst=0 | 1
sets the CMPLST ("complete list") bit in the FORMAT UNIT cdb to
0 or 1. The default is 1 in which case the existing GLIST
(grown list) is ignored. If the value is 0 then the existing
GLIST is taken into account. See the LISTS section below. Active
when the --format option is given. In most cases this bit should
be left set; some MO disk drives need this bit cleared. The SCSI
to ATA Translation (SAT) standard (prior draft: sat-r09)
requires this bit to be cleared.
where COUNT is the number of blocks to be formatted or media to
be resized to. Can be used with either --format or --resize.
With --format this option need not be given in which case it is
assumed to be zero. With --format the interpretation of COUNT
(COUNT > 0) : only format the first COUNT blocks and READ
CAPACITY will report COUNT blocks after format
(COUNT = 0) and block size unchanged : use existing block
(COUNT = 0) and block size changed : recommended maximum block
count for new block size
(COUNT = -1) : use recommended maximum block count
(COUNT < -1) : illegal
With --resize this option must be given and COUNT has this
(COUNT > 0) : after resize READ CAPACITY will report COUNT
(COUNT = 0) : after resize READ CAPACITY will report 0 blocks
(COUNT = -1) : after resize READ CAPACITY will report its
maximum number of blocks
(COUNT < -1) : illegal
In both cases if the given COUNT exceeds the maximum number of
blocks (for the block size) then the disk reports an error. See
NOTES section below.
this option sets the DCRT bit in the FORMAT UNIT command’s
parameter list header. It will "disable certification".
Certification verifies that blocks are usable during the format
process. Using this option may speed the format. The default
action of this utility (i.e. when this option is not given) is
to clear the DCRT bit thereby requesting "media certification".
When the DCRT bit is set, the FOV bit must also be set hence
sg_format does that.
this option is active when --format is given. The default action
of this utility is to poll the disk every 30 seconds to
determine the progress of the format operation until it is
finished. When this option is given this utility will exit
"early" as soon as the format has commenced. Then the user can
monitor the progress of the ongoing format operation with other
utilities (e.g. sg_turs(8) or sg_requests(8)). This option and
--wait cannot both be given.
sets the FMTPINFO field in the FORMAT UNIT cdb to a value
between 0 and 3. The default value is 0. The FMTPINFO field
from SBC-3 revision 16 is a 2 bit field (bits 7 and 6 of byte 1
in the cdb). Prior to that it was a single bit field (bit 7 of
byte 1 in the cdb) and there was an accompanying bit called
RTO_REQ (bit 6 of byte 1 in the cdb). The deprecated options
"--pinfo" and "--rto-req" represent the older usage. This option
should be used in their place. This option has no action unless
--format is given.
issue a SCSI FORMAT UNIT command. This will destroy all the
data held on the media. This option is required to change the
block size of a disk. The user is given a 10 second count down
to ponder the wisdom of doing this, during which time control-C
(amongst other Unix commands) can be used to kill this process
before it does any damage. See NOTES section for implementation
details and EXAMPLES section for typical use.
print out the usage information then exit.
the default action of this utility is to assume 32 bit logical
block addresses. With 512 byte block size this permits almost 2
terabytes (almost 2 ** 41 bytes) on a single disk. This option
selects commands and parameters that allow for 64 bit logical
block addresses. Specifically this option sets the "longlba"
flag in the MODE SENSE (10) command and uses READ CAPACITY (16)
rather than READ CAPACITY (10). This option does not set the
LONGLIST bit in the FORMAT UNIT command. The LONGLIST bit is set
as required depending other parameters (e.g. when ’--pie=PIE’ is
greater than zero).
sets the "Protection Field Usage" field in the parameter block
associated with a FORMAT UNIT command to PFU. The default value
is 0, the only other defined value currently is 1. Used together
with --fmtpinfo=FPI to specify the "protection type" to format
the disk to (see SBC-3).
The option is deprecated, use the --fmtpinfo=FPI option instead.
If used, then it sets bit 7 of byte 1 in the FORMAT UNIT cdb.
Has no action unless --format is given.
sets the "Protection Interval Exponent" field in the parameter
block associated with a FORMAT UNIT command to PIE. The default
value is 0. This field first appeared in SBC-3 revision 18. Has
no action unless --format is given.
rather than format the disk, it can be resized. This means
changing the number of blocks on the device reported by the READ
CAPACITY command. This option should be used with the
--count=COUNT option. The contents of all logical blocks on the
media remain unchanged when this option is used. This means that
any resize operation can be reversed. This option cannot be used
together with either --format or a --size=SIZE whose argument is
different to the existing block size.
The option is deprecated, use the --fmtpinfo=FPI option instead.
If used, then it sets bit 6 of byte 1 in the FORMAT UNIT cdb.
Has no action unless --format is given.
sets the "Security Initialization" (SI) bit in the FORMAT UNIT
command’s initialization pattern descriptor within the parameter
list. According to SBC-3 the default initialization pattern
"shall be written using a security erasure write technique". The
SI bit is found in SBC (1998) and SBC-2 (2005) so vendors should
support it. SATA and parallel ATA disks have a separate command
called SECURITY ERASE UNIT to perform this action. Recent
versions of the hdparm utility can execute that ATA command.
Use 6 byte variants of MODE SENSE and MODE SELECT. The default
action is to use the 10 byte variants. Some MO drives need this
option set when doing a format.
where SIZE is the block size (i.e. number of bytes in each
block) to format the device to. The default value is whatever
is currently reported by the block descriptor in a MODE SENSE
command. This option is only active when the --format option is
also given. If the block size given by this option is different
from the current value then a MODE SELECT command is used to
change it prior to the FORMAT UNIT command being started (as
recommended in the draft standard). Recent SCSI disks usually
have 512 byte sectors by default and allow up to 16 bytes extra
in a sector (i.e. 528 byte sectors). If the given size in
unacceptable to the disk, most likely an "Invalid field in
parameter list" message will appear in sense data (requires the
use of ’-v’ to decode sense data).
increase the level of verbosity, (i.e. debug output). "-vvv"
gives the maximum debug output.
print the version string and then exit.
this option only has an effect when used together with the
--format option. The default format action is to set the "IMMED"
bit in the FORMAT UNIT command’s (short) parameter header. If
this option (i.e. --wait) is given then the "IMMED" bit is not
set. If --wait is given the FORMAT UNIT command waits until the
format operation completes before returning its response. This
can be several hours on large disks. This utility sets a four
hour timeout on such a FORMAT UNIT command.
The SBC-3 draft (revision 18) defines PLIST, CLIST, DLIST and GLIST in
section 4.10 on "Medium defects". Briefly, the PLIST is the "primary"
list of manufacturer detected defects, the CLIST ("certification" list)
contains those detected during the format operation, the DLIST is a
list of defects that can be given to the format operation. The GLIST is
the grown list which starts in the format process as CLIST+DLIST and
can "grow" later due to automatic reallocation (see the ARRE and AWRE
bits in the read-write error recovery mode page (see sdparm(8))) and
use of the SCSI REASSIGN BLOCKS command (see sg_reassign(8)).
The CMPLST bit (controlled by the --cmplst=0|1 option) determines
whether the existing GLIST, when the format operation is invoked, is
taken into account. The sg_format utility sets the FOV bit to zero
which causes DPRY=0, so the PLIST is taken into account, and DCRT=0, so
the CLIST is generated and used during the format process.
The sg_format utility does not permit a user to provide a defect list
The SBC-2 standard states that the REQUEST SENSE command should be used
for obtaining a progress indication when the format command is
underway. However, tests on a selection of recent disks shows that
TEST UNIT READY commands yield progress indications (but not REQUEST
SENSE commands). So the current version of this utility uses TEST UNIT
READY commands to poll the disk to find out the progress of the format.
A new option may be required to handle this when disks catch up.
When the --format option is given without the --wait option then the
SCSI FORMAT UNIT command is issued with the IMMED bit set which causes
the SCSI command to return after it has started the format operation.
The --early option will cause sg_format to exit at that point.
Otherwise the DEVICE is polled every 30 seconds with TEST UNIT READY
commands until it reports an "all clear" (i.e. the format operation has
completed). Normally these polling commands will result in a progress
indicator (expressed as a percentage) being output to the screen. If
the user gets bored watching the progress report then sg_format process
can be terminated (e.g. with control-C) without affecting the format
operation which continues. However a bus or device reset (or a power
cycle) will probably cause the device to become "format corrupt".
When the --format and --wait options are both given then this utility
may take a long time to return. In this case care should be taken not
to send any other SCSI commands to the disk as it may not respond
leaving those commands queued behind the active format command. This
may cause a timeout in the OS driver (in a lot shorter period than 4
hours applicable to some format operations). This may result in the OS
resetting the disk leaving the format operation incomplete. This may
leave the disk in a "format corrupt" state requiring another format to
remedy the situation.
When the block size (i.e. the number of bytes in each block) is changed
on a disk two SCSI commands must be sent: a MODE SELECT to change the
block size followed by a FORMAT command. If the MODE SELECT command
succeeds and the FORMAT fails then the disk may be in a state that the
draft standard calls "format corrupt". A block descriptor in a
subsequent MODE SENSE will report the requested new block size while a
READ CAPACITY command will report the existing (i.e. different) block
size. Alternatively the READ CAPACITY command may fail, reporting the
device is not ready, potentially requiring a format. The solution to
this situation is to do a format again (and this time the new block
size does not have to be given) or change the block size back to the
The SBC-2 standard states that the block count can be set back to the
manufacturer’s maximum recommended value in a format or resize
operation. This can be done by placing an address of 0xffffffff (or the
64 bit equivalent) in the appropriate block descriptor field to a MODE
SELECT command. In signed (two’s complement) arithmetic that value
corresponds to ’-1’. So a --count=-1 causes the block count to be set
back to the manufacturer’s maximum recommended value. To see exactly
which SCSI commands are being executed and parameters passed add "-vvv"
to the sg_format command line.
Short stroking is a technique to trade off capacity for performance.
Disk performance is usually highest on the outer tracks (i.e. lower
logical block addresses) so by resizing or reformatting a disk to a
smaller capacity, average performance will usually be increased.
Other utilities may be useful in finding information associated with
formatting. These include sg_inq(8) to fetch standard INQUIRY
information (e.g. the PROTECT bit) and to fetch the extended INQUIRY
VPD page (e.g. RTO and GRD_CHK bits). The sdparm(8) utility can be used
to access and potentially change the now obsolete format mode page.
scsiformat is another utility available for formatting SCSI disks with
linux. It dates from 1997 (most recent update) and may be useful for
disks whose firmware is of that vintage.
The COUNT numeric argument may include a multiplicative suffix or be
given in hexadecimal. See the "NUMERIC ARGUMENTS" section in the
sg3_utils(8) man page.
In the first example below simply find out the existing block count and
size derived from two sources: a block descriptor in a MODE SELECT
command response and from the response of a READ CAPACITY commands. No
changes are made:
Now a simple format, leaving the block count and size as they were
previously. The FORMAT UNIT command is executed in IMMED mode and the
device is polled every 30 seconds to print out a progress indication:
sg_format --format /dev/sdm
Now the same format, but waiting (passively) until the format operation
sg_format --format --wait /dev/sdm
Next is a format in which the block size is changed to 520 bytes and
the block count is set to the manufacturer’s maximum value (for that
block size). Note, not all disks support changing the block size:
sg_format --format --size=520 /dev/sdm
Now a resize operation so that only the first 0x10000 (65536) blocks on
a disk are accessible. The remaining blocks remain unaltered.
sg_format --resize --count=0x10000 /dev/sdm
Now resize the disk back to its normal (maximum) block count:
sg_format --resize --count=-1 /dev/sdm
Format with type 1 protection:
sg_format --format --fmtpinfo=3 --pfu /dev/sdm
The exit status of sg_format is 0 when it is successful. Otherwise see
the sg3_utils(8) man page. Unless the --wait option is given, the exit
status may not reflect the success of otherwise of the format. Using
sg_turs(8) and sg_readcap(8) after the format operation may be wise.
Written by Grant Grundler, James Bottomley and Douglas Gilbert.
Report bugs to <dgilbert at interlog dot com>.
Copyright © 2005-2009 Grant Grundler, James Bottomley and Douglas
This software is distributed under the GPL version 2. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR
sg_turs(8), sg_requests(8), sg_inq(8), sg_modes(8), sg_vpd(8),
sg_reassign(8), sg_readcap(8) [all in sg3_utils], sdparm(8), scsiformat