mkfs.xfs(8) System Manager's Manual mkfs.xfs(8)
mkfs.xfs - construct an XFS filesystem
mkfs.xfs [ -b block_size ] [ -d data_section_options ] [ -f ] [ -i inode_options ] [ -l log_section_options ] [ -n naming_options ] [ -p
protofile ] [ -q ] [ -r realtime_section_options ] [ -s sector_size ] [ -L label ] [ -N ] [ -K ] device
mkfs.xfs constructs an XFS filesystem by writing on a special file using the values found in the arguments of the command line. It is
invoked automatically by mkfs(8) when it 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:
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 option elements in the argument list above can be given as multiple comma-separated suboptions if multiple suboptions apply to
the same option. Equivalently, each main option can be given multiple times with different suboptions. For example, -l inter-
nal,size=10000b and -l internal -l size=10000b are equivalent.
In the descriptions below, sizes are given in sectors, bytes, blocks, kilobytes, megabytes, gigabytes, etc. Sizes are treated as hexadeci-
mal if prefixed by 0x or 0X, octal if prefixed by 0, or decimal otherwise. The following lists possible multiplication suffixes:
s - multiply by sector size (default = 512, see -s option below).
b - multiply by filesystem block size (default = 4K, see -b option below).
k - multiply by one kilobyte (1,024 bytes).
m - multiply by one megabyte (1,048,576 bytes).
g - multiply by one gigabyte (1,073,741,824 bytes).
t - multiply by one terabyte (1,099,511,627,776 bytes).
p - multiply by one petabyte (1,024 terabytes).
e - multiply by one exabyte (1,048,576 terabytes).
This option specifies the fundamental block size of the filesystem. The valid block_size_options are: log=value or size=value and
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 KiB), the minimum is 512, and the maximum is 65536 (64 KiB). XFS on Linux currently only supports
pagesize or smaller blocks.
These options specify the location, size, and other parameters of the data section of the filesystem. The valid data_section_options
This 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 allo-
cating blocks and inodes. The minimum allocation group size is 16 MiB; the maximum size is just under 1 TiB. The data
section of the filesystem is divided into value allocation groups (default value is scaled automatically based on the
underlying device size).
This is an alternative to using the agcount suboption. The value 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 16MiB, and no more than 1TiB, and may be automatically adjusted to properly align with the stripe geometry.
The agcount and agsize suboptions are mutually exclusive.
This 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.
This is used to specify that the file given by the name suboption is a regular file. The value is either 0 or 1, with 1
signifying that the file is regular. This suboption is used only to make a filesystem image. If the value is omitted
then 1 is assumed.
This 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.
This is used to specify the stripe unit for a RAID device or a logical volume. The 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 512KiB. Also
inode allocations and the internal log will be stripe unit aligned.
This 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 value has to be specified in bytes, (usually using the m or g suffixes). This value must be
a multiple of the filesystem block size.
This is used to specify the stripe width for a RAID device or a striped logical volume. The value has to be specified in
512-byte block units. Use the sw suboption to specify the stripe width size in bytes. This suboption is required if -d
sunit has been specified and it has to be a multiple of the -d sunit suboption.
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 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 logical volume for appro-
priate sunit and swidth values.
-f Force overwrite when an existing filesystem is detected on the device. By default, mkfs.xfs will not write to the device if it sus-
pects that there is a filesystem or partition table on the device already.
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 inode_options are:
size=value | log=value | perblock=value
The inode size is specified either as a value in bytes with size=, a base two logarithm value with log=, or as the num-
ber fitting in a filesystem block with perblock=. The mininum (and default) value is 256 bytes. The maximum value is
2048 (2 KiB) 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 (on 32
bit hardware platforms) 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.
This specifies the maximum percentage of space in the filesystem that can be allocated to inodes. The default value is
25% for filesystems under 1TB, 5% for filesystems under 50TB and 1% for filesystems over 50TB.
In the default inode allocation mode, inode blocks are chosen such that inode numbers will not exceed 32 bits, which
restricts the inode blocks to the lower portion of the filesystem. The data block allocator will avoid these low blocks
to accommodate the specified maxpct, so a high value may result in a filesystem with nothing but inodes in a significant
portion of the lower blocks of the filesystem. (This restriction is not present when the filesystem is mounted with the
inode64 option on 64-bit platforms).
Setting the value to 0 means that essentially all of the filesystem can become inode blocks, subject to inode32 restric-
This value can be modified with xfs_growfs(8).
This 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 established 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 without XFS patches).
This is used to specify the version of extended attribute inline allocation policy to be used. By default, this is 2,
which uses an efficient algorithm for managing the available inline inode space between attribute and extent data.
The previous version 1, which has fixed regions for attribute and extent data, is kept for backwards compatibility with
kernels older than version 2.6.16.
This is used to enable 32bit quota project identifiers. The value is either 0 or 1, with 1 signifying that 32bit projid
are to be enabled. If the value is omitted, 0 is assumed.
These options specify the location, size, and other parameters of the log section of the filesystem. The valid log_section_options
This is used to specify that the log section is a piece of the data section instead of being another device or logical
volume. The value is either 0 or 1, with 1 signifying that the log is internal. If the value is omitted, 1 is assumed.
This is used to specify that the log section should reside on the device separate from the data section. The internal=1
and logdev options are mutually exclusive.
This 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
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 value 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 combinations of filesys-
tem block size, inode size, and directory block size, the minimum log size is larger than 512 blocks.
This specifies the version of the log. The current default is 2, which allows for larger log buffer sizes, as well as
supporting stripe-aligned log writes (see the sunit and su options, below).
The previous version 1, which is limited to 32k log buffers and does not support stripe-aligned writes, is kept for
backwards compatibility with very old 2.4 kernels.
This specifies the alignment to be used for log writes. The value has to be specified in 512-byte block units. Use the
su suboption to specify the log stripe unit size in bytes. Log writes will be aligned on this boundary, and rounded up
to this boundary. This gives major improvements in performance on some configurations such as software RAID5 when the
sunit is specified as the filesystem block size. The equivalent byte value must be a multiple of the filesystem block
size. Version 2 logs are automatically selected if the log sunit suboption is specified.
The su suboption is an alternative to using sunit.
This is used to specify the log stripe. The 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.
This changes the method of logging various persistent counters in the superblock. Under metadata intensive workloads,
these counters are updated and logged frequently enough that the superblock updates become a serialisation point in the
filesystem. The value can be either 0 or 1.
With lazy-count=1, the superblock is not modified or logged on every change of the persistent counters. Instead, enough
information is kept in other parts of the filesystem to be able to maintain the persistent counter values without needed
to keep them in the superblock. This gives significant improvements in performance on some configurations. The default
value is 1 (on) so you must specify lazy-count=0 if you want to disable this feature for older kernels which don't sup-
These options specify the version and size parameters for the naming (directory) area of the filesystem. The valid naming_options
size=value | log=value
The block size is specified either as a value in bytes with size=, or as a base two logarithm value with log=. The
block size must be a power of 2 and cannot be less than the filesystem block size. The default size value for version 2
directories is 4096 bytes (4 KiB), 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.
The naming (directory) version value can be either 2 or 'ci', defaulting to 2 if unspecified. With version 2 directo-
ries, the directory block size can be any power of 2 size from the filesystem block size up to 65536.
The version=ci option enables ASCII only case-insensitive filename lookup and version 2 directories. Filenames are case-
preserving, that is, the names are stored in directories using the case they were created with.
Note: Version 1 directories are not supported.
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 syntax of
the protofile is defined by a number of tokens separated by spaces or newlines. Note that the line numbers are not part of the syn-
tax but are meant to help you in the following discussion of the file contents.
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
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
Line 1 is a dummy string. (It was formerly the bootfilename.) It is present for backward compatibility; 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 values must appear at this point for the proto file to be correctly parsed, but their values are immaterial since they
The lines 3 through 11 specify the files and directories you want to include in this filesystem. Line 3 defines the root directory.
Other directories and files that you want in the filesystem are indicated by lines 4 through 6 and lines 8 through 10. Line 11 con-
tains symbolic link syntax.
Notice the dollar sign ($) syntax on line 7. This syntax directs the mkfs.xfs command to terminate the branch of the filesystem it
is currently on and then continue from the directory specified by the next line, in this case line 8. 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 provide the following:
* file mode
* user ID
* group ID
* the file's beginning contents
A 6-character string defines the mode for a file. The first character of this string defines the file type. The character range for
this first character is -bcdpl. A file may be a regular file, a block special file, a character special file, directory files,
named pipes (first-in, first out files), and symbolic links. The second character of the mode string is used to specify setuserID
mode, in which case it is u. If setuserID mode is not specified, the second character is -. The third character of the mode string
is used to specify the setgroupID mode, in which case it is g. If setgroupID mode is not specified, the third character is -. The
remaining characters of the mode string are a three digit octal number. This octal number defines the owner, group, and other read,
write, and execute permissions for the file, respectively. For more information on file permissions, see the chmod(1) command.
Following the mode character string are two decimal number tokens that specify the user and group IDs of the file's owner.
In a regular file, the next token specifies the pathname from which the contents and size of the file are copied. In a block or
character special file, the next token are two decimal numbers that specify the major and minor device numbers. When a file is a
symbolic link, the next token specifies the contents of the link.
When the file is a directory, the mkfs.xfs command creates the entries dot (.) and dot-dot (..) and then reads the list of names and
file specifications in a recursive manner for all of the entries in the directory. A scan of the protofile is always terminated with
the dollar ( $ ) token.
-q Quiet option. Normally mkfs.xfs prints the parameters of the filesystem to be constructed; the -q flag suppresses this.
These options specify the location, size, and other parameters of the real-time section of the filesystem. The valid realtime_sec-
This is used to specify the device which should contain the real-time section of the filesystem. The suboption value is
the name of a block device.
This is used to specify the size of the blocks in the real-time section of the filesystem. This value must be a multiple
of the filesystem block size. The minimum allowed size is the filesystem block size or 4 KiB (whichever is larger); the
default size is the stripe width for striped volumes or 64 KiB for non-striped volumes; the maximum allowed size is 1
GiB. The real-time extent size should be carefully chosen to match the parameters of the physical media used.
This is used to specify the size of the real-time section. This suboption is only needed if the real-time section of
the filesystem should occupy less space than the size of the partition or logical volume containing the section.
This option specifies the fundamental sector size of the filesystem. The sector_size is specified either as a value in bytes with
size=value or as a base two logarithm value with log=value. The default sector_size is 512 bytes. The minimum value for sector size
is 512; the maximum is 32768 (32 KiB). The sector_size must be a power of 2 size and cannot be made larger than the filesystem block
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 proceed with creating the filesystem. Refer to the mount(8) and xfs_admin(8) manual entries for additional information.
-N Causes the file system parameters to be printed out without really creating the file system.
-K Do not attempt to discard blocks at mkfs time.
xfs(5), mkfs(8), mount(8), xfs_info(8), xfs_admin(8).
With a prototype file, it is not possible to specify hard links.