sg_format man page on Scientific
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SG_FORMAT(8) SG3_UTILS SG_FORMAT(8)
NAME
sg_format - format or resize a SCSI disk (perhaps change its block
size)
SYNOPSIS
sg_format [--cmplst=0|1] [--count=COUNT] [--dcrt] [--early] [--fmt‐
pinfo=FPI] [--format] [--help] [--long] [--pfu=PFU] [--pie=PIE]
[--pinfo] [--resize] [--rto_req] [--security] [--six] [--size=SIZE]
[--verbose] [--version] [--wait] DEVICE
DESCRIPTION
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 recom‐
mends. The manufacturer's recommendation typically leaves aside a cer‐
tain 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 accessi‐
ble 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_for‐
mat. 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 "Pro‐
tection Field Usage" in the parameter header are associated with pro‐
tection information and can be set by this utility.
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.
-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.
-c, --count=COUNT
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
is:
(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
(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
interpretation:
(COUNT > 0) : after resize READ CAPACITY will report COUNT
blocks
(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.
-D, --dcrt
this option sets the DCRT bit in the FORMAT UNIT command's
parameter list header. It will "disable certification". Certifi‐
cation 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.
-e, --early
this option is active when --format is given. The default action
of this utility is to poll the disk every 30 seconds to deter‐
mine 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 can‐
not both be given.
-f, --fmtpinfo=FPI
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.
-F, --format
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.
-h, --help
print out the usage information then exit.
-l, --long
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).
-P, --pfu=PFU
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).
-p, --pinfo
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.
-q, --pie=PIE
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.
-r, --resize
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.
-R, --rto_req
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.
-S, --security
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 ver‐
sions of the hdparm utility can execute that ATA command.
-6, --six
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.
-s, --size=SIZE
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 unac‐
ceptable 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).
-v, --verbose
increase the level of verbosity, (i.e. debug output). "-vvv"
gives the maximum debug output.
-V, --version
print the version string and then exit.
-w, --wait
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.
LISTS
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
(i.e. DLIST).
NOTES
The SBC-2 standard states that the REQUEST SENSE command should be used
for obtaining a progress indication when the format command is under‐
way. 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. Other‐
wise the DEVICE is polled every 30 seconds with TEST UNIT READY com‐
mands 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 leav‐
ing 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 reset‐
ting 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 subse‐
quent 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 sit‐
uation 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 original
size.
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 opera‐
tion. 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 cor‐
responds 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 informa‐
tion (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.
EXAMPLES
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 com‐
mand response and from the response of a READ CAPACITY commands. No
changes are made:
sg_format /dev/sdm
Now a simple format, leaving the block count and size as they were pre‐
viously. 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
is complete:
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
EXIT STATUS
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.
AUTHORS
Written by Grant Grundler, James Bottomley and Douglas Gilbert.
REPORTING BUGS
Report bugs to <dgilbert at interlog dot com>.
COPYRIGHT
Copyright © 2005-2009 Grant Grundler, James Bottomley and Douglas
Gilbert
This software is distributed under the GPL version 2. There is NO war‐
ranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PUR‐
POSE.
SEE ALSO
sg_turs(8), sg_requests(8), sg_inq(8), sg_modes(8), sg_vpd(8), sg_reas‐
sign(8), sg_readcap(8) [all in sg3_utils], sdparm(8), scsiformat (old),
hdparm(8)
sg3_utils-1.27 March 2009 SG_FORMAT(8)
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