mkfs.xfs - construct an XFS filesystem
SYNOPSIS
mkfs.xfs [ -b subopt=value ] [ -d subopt[=value] ]
[ -i subopt=value ] [ -l subopt[=value] ]
[ -n subopt[=value] ] [ -p protofile ] [ -q ]
[ -r subopt[=value] ] [ -C ] [ -L label ] device
DESCRIPTION
mkfs.xfs constructs an XFS filesystem by writing on a spe
cial file using the values found in the arguments of the
command line. It is invoked automatically by mkfs(8) when
mkfs is given the -t xfs option.
In its simplest (and most commonly used form), the size of
the filesystem is determined from the disk driver. As an
example, to make a filesystem with an internal log on the
first partition on the first SCSI disk, use:
mkfs.xfs /dev/sda1
The metadata log can be placed on another device to reduce
the number of disk seeks. To create a filesystem on the
first partition on the first SCSI disk with a 10000 block
log located on the first partition on the second SCSI
disk, use:
mkfs.xfs -l logdev=/dev/sdb1,size=10000b /dev/sda1
Each of the subopt=value elements in the argument list
above can be given as multiple comma-separated sub
opt=value suboptions if multiple suboptions apply to the
same option. Equivalently, each main option can be given
multiple times with different suboptions. For example, -l
internal,size=10000b and -l internal -l size=10000b are
equivalent.
In the descriptions below, sizes are given in sectors,
bytes, blocks, kilobytes, megabytes, or gigabytes. Sizes
are treated as hexadecimal if prefixed by 0x or 0X, octal
if prefixed by 0, or decimal otherwise. If suffixed with
s then the size is converted by multiplying it by 512
(sector size). If suffixed with b then the size is con
verted by multiplying it by the filesystem's block size.
If suffixed with k then the size is converted by multiply
ing it by 1024. If suffixed with m then the size is con
verted by multiplying it by 1048576 (1024 * 1024). If
suffixed with g then the size is converted by multiplying
it by 1073741824 (1024 * 1024 * 1024).
-b Block size options.
This option specifies the fundamental block size of
log=value and size=value; only one can be supplied.
The block size is specified either as a base two
logarithm value with log=, or in bytes with size=.
The default value is 4096 bytes (4 KB) on systems
with a 4KB pagesize. The minimum value for block
size is 512; the maximum is 65536 (64 KB). XFS on
Linux currently only supports pagesize or smaller
blocks.
-d Data section options.
These options specify the location, size, and other
parameters of the data section of the filesystem.
The valid suboptions are: agcount=value,
agsize=value, file[=value], name=value, size=value,
sunit=value, swidth=value, su=value, sw=value, and
unwritten[=value].
The agcount suboption is used to specify the number
of allocation groups. The data section of the
filesystem is divided into allocation groups to
improve the performance of XFS. More allocation
groups imply that more parallelism can be achieved
when allocating blocks and inodes. The minimum
allocation group size is 16 MB; the maximum size is
just under 4 GB. The data section of the filesys
tem is divided into agcount allocation groups
(default value 8, unless the filesystem is smaller
than 128 MB or larger than 8 GB). Setting agcount
to a very large number should be avoided, since
this causes an unreasonable amount of CPU time to
be used when the filesystem is close to full.
The agsize suboption is an alternative to using
agcount. The argument provided to agsize is the
desired size of the allocation group expressed in
bytes (usually using the m or g suffixes). This
value must be a multiple of the filesystem block
size, and must be at least 16MB, and no more than
4GB, and may be automatically adjusted to properly
align with the stripe geometry. The agcount subop
tion and the agsize suboption are mutually exclu
sive.
The name suboption can be used to specify the name
of the special file containing the filesystem. In
this case, the log section must be specified as
internal (with a size, see the -l option below) and
there can be no real-time section.
The file suboption is used to specify that the file
given by the name suboption is a regular file. The
suboption value is either 0 or 1, with 1 signifying
only to make a filesystem image. If the value is
omitted then 1 is assumed.
The size suboption is used to specify the size of
the data section. This suboption is required if -d
file[=1] is given. Otherwise, it is only needed if
the filesystem should occupy less space than the
size of the special file.
The sunit suboption is used to specify the stripe
unit for a RAID device or a logical volume. The
suboption value has to be specified in 512-byte
block units. Use the su suboption to specify the
stripe unit size in bytes. This suboption ensures
that data allocations will be stripe unit aligned
when the current end of file is being extended and
the file size is larger than 512KB. Also inode
allocations and the internal log will be stripe
unit aligned.
The su suboption is an alternative to using sunit.
The su suboption is used to specify the stripe unit
for a RAID device or a striped logical volume. The
suboption value has to be specified in bytes, (usu
ally using the m or g suffixes). This value must
be a multiple of the filesystem block size.
The swidth suboption is used to specify the stripe
width for a RAID device or a striped logical vol
ume. The suboption value has to be specified in
512-byte block units. Use the sw suboption to
specify the stripe width size in bytes. This sub
option is required if -d sunit has been specified
and it has to be a multiple of the -d sunit subop
tion. The stripe width will be the preferred
iosize returned in the stat(2) system call.
The sw suboption is an alternative to using swidth.
The sw suboption is used to specify the stripe
width for a RAID device or striped logical volume.
The suboption value is expressed as a multiplier of
the stripe unit, usually the same as the number of
stripe members in the logical volume configuration,
or data disks in a RAID device.
When a filesystem is created on a logical volume
device, mkfs.xfs will automatically query the logi
cal volume for appropriate sunit and swidth values.
The unwritten suboption is used to specify whether
unwritten extents are flagged as such, or not. The
suboption value is either 0 or 1, with 1 signifying
that unwritten extent flagging should occur. If
is enabled. If unwritten extents are flagged,
filesystem write performance will be negatively
affected for preallocated file extents, since extra
filesystem transactions are required to convert
extent flags for the range of the file written.
This suboption should be disabled if the filesystem
needs to be used on operating system versions which
do not support the flagging capability.
-i Inode options.
This option specifies the inode size of the
filesystem, and other inode allocation parameters.
The XFS inode contains a fixed-size part and a
variable-size part. The variable-size part, whose
size is affected by this option, can contain:
directory data, for small directories; attribute
data, for small attribute sets; symbolic link data,
for small symbolic links; the extent list for the
file, for files with a small number of extents; and
the root of a tree describing the location of
extents for the file, for files with a large number
of extents.
The valid suboptions for specifying inode size are:
log=value, perblock=value, and size=value; only one
can be supplied. The inode size is specified
either as a base two logarithm value with log=, in
bytes with size=, or as the number fitting in a
filesystem block with perblock=. The mininum (and
default) value is 256 bytes. The maximum value is
2048 (2 KB) subject to the restriction that the
inode size cannot exceed one half of the filesystem
block size.
XFS uses 64-bit inode numbers internally; however,
the number of significant bits in an inode number
is affected by filesystem geometry. In practice,
filesystem size and inode size are the predominant
factors. The Linux kernel and most applications
cannot currently handle inode numbers greater than
32 significant bits, so if no inode size is given
on the command line, mkfs.xfs will attempt to
choose a size such that inode numbers will be < 32
bits. If an inode size is specified, or if a
filesystem is sufficently large, mkfs.xfs will warn
if this will create inode numbers > 32 significant
bits.
The option maxpct=value specifies the maximum per
centage of space in the filesystem that can be
allocated to inodes. The default value is 25%.
Setting the value to 0 means that essentially all
The option align[=value] is used to specify that
inode allocation is or is not aligned. The value
is either 0 or 1, with 1 signifying that inodes are
allocated aligned. If the value is omitted, 1 is
assumed. The default is that inodes are aligned.
Aligned inode access is normally more efficient
than unaligned access; alignment must be estab
lished at the time the filesystem is created, since
inodes are allocated at that time. This option can
be used to turn off inode alignment when the
filesystem needs to be mountable by a version of
IRIX that does not have the inode alignment feature
(any release of IRIX before 6.2, and IRIX 6.2 with
out XFS patches).
-l Log section options.
These options specify the location, size, and other
parameters of the log section of the filesystem.
The valid suboptions are: internal[=value],
size=value, version=[1|2], sunit=value, and
su=value.
The internal suboption is used to specify that the
log section is a piece of the data section instead
of being another device or logical volume. The
suboption value is either 0 or 1, with 1 signifying
that the log is internal. If the value is omitted,
1 is assumed.
The size suboption is used to specify the size of
the log section.
If the log is contained within the data section and
size isn't specified, mkfs.xfs will try to select a
suitable log size depending on the size of the
filesystem. The actual logsize depends on the
filesystem block size and the directory block size.
Otherwise, the size suboption is only needed if the
log section of the filesystem should occupy less
space than the size of the special file. The size
is specified in bytes or blocks, with a b suffix
meaning multiplication by the filesystem block
size, as described above. The overriding minimum
value for size is 512 blocks. With some combina
tions of filesystem block size, inode size, and
directory block size, the minimum log size is
larger than 512 blocks.
Using the version suboption to specify a version 2
log enables the sunit suboption, and allows the
logs are automatically selected if a log stripe
unit is specified. See sunit and su suboptions,
below.
The sunit suboption specifies the alignment to be
used for log writes. The suboption value has to be
specified in 512-byte block units. Use the su sub
option to specify the log stripe unit size in
bytes. Log writes will be aligned on this bound
ary, and rounded up to this boundary. This gives
major improvements in performance on some configu
rations such as software raid5 when the sunit is
specified as the filesystem block size. The equiv
alent byte value must be a multiple of the filesys
tem block size. Version 2 logs are automatically
selected if the log su suboption is specified.
The su suboption is an alternative to using sunit.
The su suboption is used to specify the log stripe.
The suboption value has to be specified in bytes,
(usually using the s or b suffixes). This value
must be a multiple of the filesystem block size.
Version 2 logs are automatically selected if the
log su suboption is specified.
-n Naming options.
These options specify the version and size parame
ters for the naming (directory) area of the
filesystem. The valid suboptions are: log=value,
size=value, and version=value. The naming (direc
tory) version is 1 or 2, defaulting to 2 if unspec
ified. With version 2 directories, the directory
block size can be any power of 2 size from the
filesystem block size up to 65536. The block size
is specified either as a base two logarithm value
with log=, or in bytes with size=. The default
size value for version 2 directories is 4096 bytes
(4 KB), unless the filesystem block size is larger
than 4096, in which case the default value is the
filesystem block size. For version 1 directories
the block size is the same as the filesystem block
size.
-p protofile
If the optional -p protofile argument is given,
mkfs.xfs uses protofile as a prototype file and
takes its directions from that file. The blocks
and inodes specifiers in the protofile are provided
for backwards compatibility, but are otherwise
unused. The prototype file contains tokens sepa
rated by spaces or newlines. A sample prototype
specification follows (line numbers have been added
1 /stand/diskboot
2 4872 110
3 d--777 3 1
4 usr d--777 3 1
5 sh ---755 3 1 /bin/sh
6 ken d--755 6 1
7 $
8 b0 b--644 3 1 0 0
9 c0 c--644 3 1 0 0
10 fifo p--644 3 1
11 slink l--644 3 1 /a/symbolic/link
12 : This is a comment line
13 $
14 $
Line 1 is a dummy string. (It was formerly the
bootfilename.) It is present for backward compati
bility; boot blocks are not used on SGI systems.
Note that some string of characters must be present
as the first line of the proto file to cause it to
be parsed correctly; the value of this string is
immaterial since it is ignored.
Line 2 contains two numeric values (formerly the
numbers of blocks and inodes). These are also
merely for backward compatibility: two numeric val
ues must appear at this point for the proto file to
be correctly parsed, but their values are immate
rial since they are ignored.
Lines 3-11 tell mkfs.xfs about files and directo
ries to be included in this filesystem. Line 3
specifies the root directory. Lines 4-6 and 8-10
specifies other directories and files. Note the
special symbolic link syntax on line 11.
The $ on line 7 tells mkfs.xfs to end the branch of
the filesystem it is on, and continue from the next
higher directory. It must be the last character on
a line. The colon on line 12 introduces a comment;
all characters up until the following newline are
ignored. Note that this means you cannot have a
file in a prototype file whose name contains a
colon. The $ on lines 13 and 14 end the process,
since no additional specifications follow.
File specifications give the mode, the user ID, the
group ID, and the initial contents of the file.
Valid syntax for the contents field depends on the
first character of the mode.
string. The first character specifies the type of
the file. The character range is -bcdpl to specify
regular, block special, character special, direc
tory files, named pipes (fifos), and symbolic
links, respectively. The second character of the
mode is either u or - to specify setuserID mode or
not. The third is g or - for the setgroupID mode.
The rest of the mode is a three digit octal number
giving the owner, group, and other read, write,
execute permissions (see chmod(1)).
Two decimal number tokens come after the mode; they
specify the user and group IDs of the owner of the
file.
If the file is a regular file, the next token of
the specification can be a pathname from which the
contents and size are copied. If the file is a
block or character special file, two decimal num
bers follow that give the major and minor device
numbers. If the file is a symbolic link, the next
token of the specification is used as the contents
of the link. If the file is a directory, mkfs.xfs
makes the entries . and .. and then reads a list
of names and (recursively) file specifications for
the entries in the directory. As noted above, the
scan is terminated with the token $.
-q Quiet option.
Normally mkfs.xfs prints the parameters of the
filesystem to be constructed; the -q flag sup
presses this.
-r Real-time section options.
These options specify the location, size, and other
parameters of the real-time section of the filesys
tem. The valid suboptions are: extsize=value and
size=value.
The extsize suboption is used to specify the size
of the blocks in the real-time section of the
filesystem. This size must be a multiple of the
filesystem block size. The minimum allowed value
is the filesystem block size or 4 KB (whichever is
larger); the default value is the stripe width for
striped volumes or 64 KB for non-striped volumes;
the maximum allowed value is 1 GB. The real-time
extent size should be carefully chosen to match the
parameters of the physical media used.
The size suboption is used to specify the size of
needed if the real-time section of the filesystem
should occupy less space than the size of the par
tition or logical volume containing the section.
-C Disable overlapping partition/volume checks.
By default mkfs.xfs checks to see if the destina
tion partition or logical volume overlaps any
mounted or reserved partitions in the system. If
an overlap or mount conflict is found, the user
will be notified and prevented from potentially
corrupting the existing data. For systems with a
large number of disks, this additional checking may
add noticable overhead to the command's execution
time. For situations where command performance is
necessary, this switch may be used to disable the
safeguards. Due to the potential for user-error
causing corrupted filesystems or other on-disk data
corruption, we strongly discourage use of this
switch in normal operation.
-L label
Set the filesystem label. XFS filesystem labels
can be at most 12 characters long; if label is
longer than 12 characters, mkfs.xfs will not pro
ceed with creating the filesystem. Refer to the
mount(8) and xfs_admin(8) manual entries for addi
tional information.
SEE ALSO
mkfs(8), mount(8), xfs_info(8), xfs_admin(8).
BUGS
With a prototype file, it is not possible to specify hard
links.
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