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SG_FORMAT(8) SG3_UTILS SG_FORMAT(8)
NAME
sg_format - format, format with preset, resize SCSI disk; format tape
SYNOPSIS
sg_format [--cmplst={0|1}] [--count=COUNT] [--dcrt] [--dry-run] [--early] [--ffmt=FFMT]
[--fmtmaxlba-fmtpinfo=FPI] [--format] [--help] [--ip-def] [--long] [--mode=MP] [--pfu=PFU]
[--pie=PIE] [--pinfo] [--poll=PT] [--preset=ID] [--quick] [--resize] [--rto_req] [--secu-
rity] [--six] [--size=LB_SZ] [--tape=FM] [--timeout=SECS] [--verbose] [--verify] [--ver-
sion] [--wait] DEVICE
DESCRIPTION
Not all SCSI direct access devices need to be formatted and some have vendor specific for-
matting 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 blocks to logical block addresses during the life of
the disk.
This utility issues one of three SCSI format commands: FORMAT UNIT, FORMAT MEDIUM or FOR-
MAT WITH PRESET. In the following description, unqualified sections will usually be refer-
ring to the SCSI FORMAT UNIT command. Both FORMAT UNIT and FORMAT WITH PRESET apply to
disks (or disk-like devices). The FORMAT MEDIUM command is for tapes.
This utility can format modern SCSI disks and potentially change their block size (if per-
mitted) 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. There is a
Format Status log page which reports on the previous successful format operation(s).
When this utility is used without options (i.e. it is only given a DEVICE argument) 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 the NOTES section). This usage will not modify the disk.
When this utility is used with either --format, --preset=ID or --tape=FM, it will attempt
to format the given DEVICE. In the absence of the --quick option there is a 15 second
pause during which time the user is invited thrice (5 seconds apart) to abort sg_format.
This occurs just prior the SCSI FORMAT UNIT, FORMAT WITH PRESET or FORMAT MEDIUM command
being issued. See the NOTES section for more information.
Protection information (PI) is optional and is made up of one or more protection inter-
vals, each made up of 8 bytes associated with a logical block. When PI is active each log-
ical block will have 1, 2, 4, 8, etc protection intervals (i.e. a power of two), inter-
leaved with (and following) the user data to which they refer. Four protection types are
defined with protection type 0 being no protection intervals. See the PROTECTION INFORMA-
TION section below for more information.
When the --tape=FM option is given then the SCSI FORMAT MEDIUM command is sent to the DE-
VICE. FORMAT MEDIUM is defined in the SSC documents at T10 and prepares a volume for use.
That may include partitioning the medium. See the section below on TAPE for more informa-
tion.
The FORMAT WITH PRESET was added in draft SBC-4 revision 18. A preset pattern, selected by
the PRESET IDENTIFIER field (--id=FWPID), is written to the disk. See the FORMAT PRESETS
VPD page (0xb8) for a list of available Format preset identifiers and their associated
data.
OPTIONS
Arguments to long options are mandatory for short options as well. The options are ar-
ranged 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. If the
value is 0 then the existing GLIST (grown list) is taken into account. If the
value is 1 then the existing GLIST is ignored. CMPLST defaults to 1 apart from when
the --ffmt=FFMT option's value is non-zero in which case CMPLST defaults to 0. See
the LISTS section below. In most cases this bit should be left at its default
value.
-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". Certification verifies that blocks are usable dur-
ing the format process. Using this option may speed the format but --ffmt=FFMT, if
available, would probably be better. The default action of this utility (i.e. when
this option is not given) is to clear the DCRT bit thereby requesting "media certi-
fication" (also unless another option needs it, the FOV bit will be cleared). When
the DCRT bit is set, the FOV bit must also be set hence sg_format does that.
If this option is given twice then certification is enabled by clearing the DCRT
bit and setting the FOV bit. Both these bits are found in the parameter list asso-
ciated with the FORMAT UNIT cdb.
-d, --dry-run
this option will parse the command line, do all the preparation but bypass the ac-
tual FORMAT UNIT, FORMAT WITH PRESET or FORMAT MEDIUM command. Also if the options
would otherwise cause the logical block size to change, then the MODE SELECT com-
mand that would do that is also bypassed when the dry run option is given.
-e, --early
during a format operation, The default action of this utility is to poll the disk
every 60 seconds (or every 10 seconds if FFMT is non-zero) to determine the
progress of the format operation until it is finished. When this option is given
this utility will exit "early", that is as soon as the format operation has com-
menced. 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 are
mutually exclusive.
-t, --ffmt=FFMT
FFMT (fast format) is placed in a field of the same name in the FORMAT UNIT cdb.
The field was introduced in SBC-4 revision 10. The default value is 0 which implies
the former action which is typically to overwrite all blocks on the DEVICE. That
can take a long time (e.g. with hard disks over 10 TB in size that can be days).
With FFMT set that time may be reduced to minutes or less. So it is worth trying if
it is available.
FFMT has values 1 and 2 for fast format with 3 being reserved currently. These two
values include this description: "The device server initializes the medium ...
without overwriting the medium (i.e. resources for managing medium access are ini-
tialized and the medium is not written)". The difference between 1 and 2 concerns
read operations on LBAs to which no data has been written to, after the fast for-
mat. When FFMT is 1 the read operation should return "unspecified logical block
data" and complete without error. When FFMT is 2 the read operation may yield check
condition status with a sense key set to hardware error, medium error or command
aborted. See draft SBC-4 revision 16 section 4.34 for more details.
-b, --fmtmaxlba
This option is only active if it is given together with the --preset=ID option. If
so it sets the FMTMAXLBA field in the FORMAT WITH PRESET command.
-f, --fmtpinfo=FPI
sets the FMTPINFO field in the FORMAT UNIT cdb to a value between 0 and 3. The de-
fault 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 revision 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. See the PROTECTION IN-
FORMATION section below for more information.
-F, --format
issue one of the three SCSI "format" commands. In the absence of the --preset=ID
and --tape=FM options, the SCSI FORMAT UNIT command is issued. These commands will
destroy all the data held on the media. This option is required to change the
block size of a disk. In the absence of the --quick option, the user is given a 15
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.
When used three times (or more) the preliminary MODE SENSE and SELECT commands are
bypassed, leaving only the initial INQUIRY and FORMAT UNIT commands. This is for
emergency use (e.g. when the MODE SENSE/SELECT commands are not working) and cannot
change the logical block size.
See NOTES section for implementation details and EXAMPLES section for typical use.
-h, --help
print out the usage information then exit.
-I, --ip-def
sets the default Initialization Pattern. Some disks (SSDs) use this to flag that a
format should fully provision (i.e. associate a physical block with every logical
block). The same disks (SSDs) might thin provision if this option is not given. If
this option is given then the --security option cannot be given. Also accepts
--ip_def for this option.
-l, --long
the default action of this utility is to assume 32 bit logical block addresses.
With 512 byte block size this permits more than 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).
If this option is not given and READ CAPACITY (10) or MODE SELECT detects a disk
the needs more than 32 bits to represent its logical blocks then it is set inter-
nally. 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).
-M, --mode=MP
MP is a mode page number (0 to 62 inclusive) that will be used for reading and per-
haps changing the device logical block size. The default is 1 which is the
Read-Write Error Recovery mode page.
Preferably the chosen (or default) mode page should be saveable (i.e. accept the
SP bit set in the MODE SELECT command used when the logical block size is being
changed). Recent version of this utility will retry a MODE SELECT if the SP=1 vari-
ant fails with a sense key of ILLEGAL REQUEST. That retry will use the same MODE
SELECT command but with SP=0 .
-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. See the PROTECTION INFORMATION section below for more information.
-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. PIE can only be
non-zero with protection types 2 and 3. The value of 0 is typical for 512 byte
blocks; with 4096 byte blocks a value of 3 may be appropriate (i.e. 8 protection
intervals interleaved with 4096 bytes of user data). A device may not support any
non-zero values. This field first appeared in SBC-3 revision 18.
-p, --pinfo
this option is deprecated, use the --fmtpinfo=FPI option instead. If used, then it
sets bit 7 of byte 1 in the FORMAT UNIT cdb and that is equivalent to setting
--fmtpinfo=2. [So if --pinfo is used (plus --fmtpinfo=FPI and --pfu=PFU are not
given or their arguments are 0) then protection type 1 is selected.]
-x, --poll=PT
where PT is the type of poll used. If PT is 0 then a TEST UNIT READY command is
used, otherwise a REQUEST SENSE command is used. The default is currently 0 but
this will change to 1 in the near future. See the NOTES sections below.
-E, --preset=ID
this option instructs this utility to issue a SCSI FORMAT WITH PRESET command. The
PRESET IDENTIFIER field in that cdb is set to ID. The IMMED field in that cdb is
also set unless the --wait option is also given, in which case it is cleared.
-Q, --quick
the default action (i.e. when the option is not given) is to give the user 15 sec-
onds to reconsider doing a format operation on the DEVICE. When this option is
given that step (i.e. the 15 second warning period) is skipped.
-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 me-
dia 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=LB_SZ 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.
-S, --security
sets the "Security Initialization" (SI) bit in the FORMAT UNIT command's initial-
ization pattern descriptor within the parameter list. According to SBC-3 the de-
fault initialization pattern "shall be written using a security erasure write tech-
nique". See the NOTES section on the SCSI SANITIZE command. If this option is given
then the --ip_def option cannot be given.
-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=LB_SZ
where LB_SZ is the logical block size (i.e. number of user 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. 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 SBC stan-
dards). Some SCSI disks have 512 byte logical blocks by default and allow an alter-
nate logical block size of 4096 bytes. 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).
Note that formatting a disk to add or remove protection information is not regarded
as a change to its logical block size so this option should not be used.
-T, --tape=FM
will send a FORMAT MEDIUM command to the DEVICE with its FORMAT field set to FM.
This option is used to prepare a tape (i.e. the "medium") in a tape drive for use.
Values for FM include 0 to do the "default" format; 1 to partition a volume and 2
to do a default format then partition.
-m, --timeout=SECS
where SECS is the FORMAT UNIT, FORMAT WITH PRESET or FORMAT MEDIUM command timeout
in seconds. SECS will only be used if it exceeds the internal timeout which is 20
seconds if the IMMED bit is set and 72000 seconds (20 hours) or higher if the IMMED
bit is not set. If the disk size exceeds 4 TB then the timeout value is increased
to 144000 seconds (40 hours). And if it is greater than 8 TB then the timeout
value is increased to 288000 seconds (80 hours). If the timeout is exceeded then
the operating system will typically abort the command. Aborting a command may esca-
late to a LUN reset (or worse). A timeout may also leave the disk or tape format
operation incomplete. And that may result in the disk or tape being in a "format
corrupt" state requiring another format to remedy the situation. So for various
reasons command timeouts are best avoided.
-v, --verbose
increase the level of verbosity, (i.e. debug output). "-vvv" gives a lot more debug
output.
-y, --verify
set the VERIFY bit in the FORMAT MEDIUM cdb. The default is that the VERIFY bit is
clear. This option is only appropriate for tapes.
-V, --version
print the version string and then exit.
-w, --wait
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 then the FORMAT UNIT, FORMAT WITH PRESET or FOR-
MAT MEDIUM command waits until the format operation completes before returning its
response. This can be many hours on large disks. See the --timeout=SECS option.
Alternatively this option may be useful when used together with --ffmt=FFMT (and
FFMT greater than 0) since the fast format may only be a matter of seconds.
LISTS
The SBC-3 draft (revision 20) defines PLIST, CLIST, DLIST and GLIST in section 4.10 on
"Medium defects". Briefly, the PLIST is the "primary" list of manufacturer detected de-
fects, the CLIST ("certification" list) contains those detected during the format opera-
tion, 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_reas-
sign(8)).
By the SBC-3 standard (following draft revision 36) the CLIST and DLIST had been removed,
leaving PLIST and GLIST. Only PLIST and GLIST are found in the SBC-4 drafts.
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).
PROTECTION INFORMATION
Protection Information (PI) is additional information held with logical blocks so that an
application and/or host bus adapter can check the correctness of those logical blocks. PI
is placed in one or more protection intervals interleaved in each logical block. Each pro-
tection interval follows the user data to which it refers. A protection interval contains
8 bytes made up of a 2 byte "logical block guard" (CRC), a 2 byte "logical block applica-
tion guard", and a 4 byte "logical block reference tag". Devices with 512 byte logical
block size typically have one protection interval appended, making its logical block data
520 bytes long. Devices with 4096 byte logical block size often have 8 protection inter-
vals spread across its logical block data for a total size of 4160 bytes. Note that for
all other purposes the logical block size is considered to be 512 and 4096 bytes respec-
tively.
The SBC-3 standard have added several "protection types" to the PI introduced in the SBC-2
standard. SBC-3 defines 4 protection types (types 0 to 3) with protection type 0 meaning
no PI is maintained. While a device may support one or more protection types, it can only
be formatted with 1 of the 4. To change a device's protection type, it must be re-format-
ted. For more information see the Protection Information in section 4.21 of draft SBC-4
revision 16.
A device that supports PI information (i.e. supports one or more protection types 1, 2 and
3) sets the "PROTECT" bit in its standard INQUIRY response. It also sets the SPT field in
the EXTENDED INQUIRY VPD page response to indicate which protection types it supports.
Given PROTECT=1 then SPT=0 implies the device supports PI type 1 only, SPT=1 implies the
device supports PI types 1 and 2, and various other non-obvious mappings up to SPT=7 which
implies protection types 1, 2 and 3 are supported. The current protection type of a disk
can be found in the "P_TYPE" and "PROT_EN" fields in the response of a READ CAPACITY (16)
command (e.g. with the 'sg_readcap --long' utility).
Given that a device supports a particular protection type, a user can then choose to for-
mat that disk with that protection type by setting the "FMTPINFO" and "Protection Field
Usage" fields in the FORMAT UNIT command. Those fields correspond to the --fmtpinfo=FPI
and the --pfu=PFU options in this utility. The list below shows the four protection types
followed by the options of this utility needed to select them:
0 : --fmtpinfo=0 --pfu=0
1 : --fmtpinfo=2 --pfu=0
2 : --fmtpinfo=3 --pfu=0
3 : --fmtpinfo=3 --pfu=1
The default value of FPI (in --fmtpinfo=FPI) is 0 and the default value of PFU (in
--pfu=PFU) is 0. So if neither --fmtpinfo=FPI nor --pfu=PFU are given then protection type
0 (i.e. no protection information) is chosen.
NOTES
After a format that changes the logical block size or the number of logical blocks on a
disk, the operating system may need to be told to re-initialize its setting for that disk.
In Linux that can be done with:
echo 1 > /sys/block/sd{letter(s)}/device/rescan
where "letter(s)" will be between 'a' and 'zzz'. The lsscsi utility in Linux can be used
to check the various namings of a disk.
The SBC-2 standard states that the REQUEST SENSE command should be used for obtaining
progress indication when the format command is underway. However, tests on a selection of
disks shows that TEST UNIT READY commands yield progress indications (but not REQUEST
SENSE commands). So the current version of this utility defaults to using TEST UNIT READY
commands to poll the disk to find out the progress of the format. The --poll=PT option has
been added to control this.
When the --format, --preset=ID or --tape=FM option is given without the --wait option then
the corresponding SCSI command is issued with the IMMED bit set which causes the SCSI com-
mand 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 60 seconds or every
10 seconds if FFMT is non-zero. The poll is with TEST UNIT READY or REQUEST SENSE commands
until one 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 target or device reset (or a power cycle) will probably cause
the format to cease and the DEVICE to become "format corrupt".
When the --format (--preset=ID or --tape) 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 pe-
riod than 20 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 "for-
mat corrupt" state requiring another format to remedy the situation. Modern SCSI devices
should yield a "not ready" sense key with an additional sense indicating a format is in
progress. With older devices the user should take precautions that nothing attempts to ac-
cess a device while it is being formatted. Unmounting in mounted file systems on a DEVICE
prior to calling this utility is strongly advised.
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 com-
mand. If the MODE SELECT command succeeds and the FORMAT fails then the disk may be in a
state that the 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. previous) 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 original size.
The SBC-2 standard states that the block count can be set back to the manufacturer's maxi-
mum recommended value in a format or resize operation. This can be done by placing an ad-
dress 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 maxi-
mum recommended value. To see exactly which SCSI commands are being executed and parame-
ters passed add the "-vvv" option to the sg_format command line.
The FMTDATA field shown in the FORMAT UNIT cdb does not have a corresponding option in
this utility. When set in the cdb it indicates an additional parameter list will be sent
to the DEVICE along with the cdb. It is set as required, basically when any field in the
parameter list header is set.
Short stroking is a technique to trade off capacity for performance on hard disks. "Hard"
disk is often used to mean a storage device with spinning platters which contain the user
data. Solid State Disk (SSD) is the newer form of storage device that contains no moving
parts. Hard disk performance is usually highest on the outer tracks (usually the lower
logical block addresses) so by resizing or reformatting a disk to a smaller capacity, av-
erage performance will usually be increased.
Other utilities may be useful in finding information associated with formatting. These in-
clude 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 vin-
tage.
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.
The SCSI SANITIZE command was introduced in SBC-3 revision 27. It is closely related to
the ATA sanitize disk feature set and can be used to remove all existing data from a disk.
Sanitize is more likely to be implemented on modern disks (including SSDs) than FORMAT
UNIT's security initialization feature (see the --security option) and in some cases much
faster.
SSDs that support thin provisioning will typically unmap all logical blocks during a for-
mat. The reason is to improve the SSD's endurance. Also thin provisioned formats typically
complete faster than fully provisioned ones on the same disk (see the --ip_def option). In
either case format operations on SSDs tend to be a lot faster than they are on hard disks
with spinning media.
TAPE
Tape system use a variant of the FORMAT UNIT command used on disks. Tape systems use the
FORMAT MEDIUM command which is simpler with only three fields in the cdb typically used.
Apart from sharing the same opcode the cdbs of FORMAT UNIT and FORMAT MEDIUM are quite
different. FORMAT MEDIUM's fields are VERIFY, IMMED and FORMAT (with TRANSFER LENGTH al-
ways set to 0). The VERIFY bit field is set with the --verify option. The IMMED bit is
manipulated by the --wait option in the same way it is for disks; one difference is that
if the --poll=PT option is not given then it defaults to PT of 1 which means the poll is
done with REQUEST SENSE commands.
The argument given to the --tape=FM option is used to set the FORMAT field. FM can take
values from "-1" to "15" where "-1" (the default) means don't do a tape format; value "8"
to "15" are for vendor specific formats. The --early option may also be used to set the
IMMED bit and then exit this utility (rather than poll periodically until it is finished).
In this case the tape drive will still be busy doing the format for some time but, accord-
ing to T10, should still respond in full to the INQUIRY and REPORT LUNS commands. Other
commands (including REQUEST SENSE) should yield a "not ready" sense key with an additional
sense code of "Logical unit not ready, format in progress". Additionally REQUEST SENSE
should contain a progress indication in its sense data.
When FM is 1 or 2 then the settings in the Medium partition mode page control the parti-
tioning. That mode page can be viewed and modified with the sdparm utility.
Prior to invoking this utility the tape may need to be positioned to the beginning of par-
tition 0. In Linux that can typically be done with the mt utility (e.g. 'mt -f /dev/st0
rewind').
EXAMPLES
These examples use Linux device names. For suitable device names in other supported Oper-
ating Systems see 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:
# sg_format /dev/sdm
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 60 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 acces-
sible. 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
One reason to format a SCSI disk is to add protection information. First check which pro-
tection types are supported by a disk (by checking the SPT field in the Extended inquiry
VPD page together with the Protect bit in the standard inquiry response):
# sg_vpd -p ei -l /dev/sdb
extended INQUIRY data VPD page:
ACTIVATE_MICROCODE=0
SPT=1 [protection types 1 and 2 supported]
....
Format with type 1 protection:
# sg_format --format --fmtpinfo=2 /dev/sdm
After a successful format with type 1 protection, READ CAPACITY(16) should show something
like this:
# sg_readcap -l /dev/sdm
Read Capacity results:
Protection: prot_en=1, p_type=0, p_i_exponent=0 [type 1 protection]
Logical block provisioning: lbpme=0, lbprz=0
....
To format with type 3 protection:
# sg_format --format --fmtpinfo=3 --pfu=1 /dev/sdm
For the disk shown above this will probably fail because the Extended inquiry VPD page
showed only types 1 and 2 protection are supported.
Here are examples of using fast format (FFMT field in FORMAT UNIT cdb) to quickly switch
between 512 and 4096 byte logical block size. Assume disk starts with 4096 byte logical
block size and all important data has been backed up.
# sg_format --format --ffmt=1 --size=512 /dev/sdd
Now /dev/sdd should have 512 byte logical block size. And to switch it back:
# sg_format --format --ffmt=1 --size=4096 /dev/sdd
Since fast formats can be very quick (a matter of seconds) using the --wait option may be
appropriate.
And to use the Format with preset command this invocation could be used:
# sg_format --preset=1 --fmtmaxlba /dev/sdd
The FORMAT PRESETS VPD page (0xb8) should be consulted to check that Preset identifier 0x1
is there and has the expected format (i.e. "default host aware zoned block device model
with 512 bytes of user data in each logical block"). That VPD page can be viewed with the
sg_vpd utility.
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.
The Unix convention is that "no news is good news" but that can be a bit unnerving after
an operation like format, especially if it finishes quickly (i.e. before the first
progress poll is sent). Giving the --verbose option once should supply enough additional
output to settle those nerves.
AUTHORS
Written by Grant Grundler, James Bottomley and Douglas Gilbert.
REPORTING BUGS
Report bugs to <dgilbert at interlog dot com>.
COPYRIGHT
Copyright (C) 2005-2020 Grant Grundler, James Bottomley and 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.
SEE ALSO
sg_turs(8), sg_requests(8), sg_inq(8), sg_modes(8), sg_vpd(8), sg_reassign(8), sg_read-
cap(8), sg3_utils(8), sg_sanitize(8) [all in sg3_utils], lsscsi(8), mt(mt-st), sdparm(8),
scsiformat (old), hdparm(8)
sg3_utils-1.45 January 2020 SG_FORMAT(8)
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