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mkfs.xfs - construct an XFS filesystem
mkfs.xfs - construct an XFS filesystem
SYNOPSIS
mkfs.xfs [ -b block_size_options ] [ -m global_metadata_options ] [ -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_options ] [ -L label ] [ -N ] [ -K ] device
mkfs.xfs -V
DESCRIPTION
mkfs.xfs constructs an XFS filesystem by writing on a special file using the values found in the arguments of the com‐mand 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:
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 10MiB log located on the first partition on the second SCSI disk, use:
mkfs.xfs -l logdev=/dev/sdb1,size=10m /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 subop‐
tions. For example, -l internal,size=10m and -l internal -l size=10m are equivalent.
In the descriptions below, sizes are given in sectors, bytes, blocks, kilobytes, megabytes, gigabytes, etc. Sizes are
treated as hexadecimal 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).
When specifying parameters in units of sectors or filesystem blocks, the -s option or the -b option first needs to be added to the command line. Failure to specify the size of the units will result in illegal value errors when parameters are quantified in those units.
Many feature options allow an optional argument of 0 or 1, to explicitly disable or enable the functionality.
OPTIONS
-b block_size_options
This option specifies the fundamental block size of the filesystem. The valid block_size_option is:
size=value
The filesystem block size is specified with a value in bytes. The default value is 4096 bytes (4
KiB), the minimum is 512, and the maximum is 65536 (64 KiB).
To specify any options on the command line in units of filesystem blocks, this option must be spec‐
ified first so that the filesystem block size is applied consistently to all options.
Although mkfs.xfs will accept any of these values and create a valid filesystem, XFS on Linux can
only mount filesystems with pagesize or smaller blocks.
-m global_metadata_options
These options specify metadata format options that either apply to the entire filesystem or aren't easily characterised by a specific functionality group. The valid global_metadata_options arecrc=value
This is used to create a filesystem which maintains and checks CRC information in all metadata
objects on disk. The value is either 0 to disable the feature, or 1 to enable the use of CRCs.
CRCs enable enhanced error detection due to hardware issues, whilst the format changes also
improves crash recovery algorithms and the ability of various tools to validate and repair metadata
corruptions when they are found. The CRC algorithm used is CRC32c, so the overhead is dependent on
CPU architecture as some CPUs have hardware acceleration of this algorithm. Typically the overhead
of calculating and checking the CRCs is not noticeable in normal operation.
By default, mkfs.xfs will enable metadata CRCs.
finobt=value
This option enables the use of a separate free inode btree index in each allocation group. The
value is either 0 to disable the feature, or 1 to create a free inode btree in each allocation
group.
The free inode btree mirrors the existing allocated inode btree index which indexes both used and
free inodes. The free inode btree does not index used inodes, allowing faster, more consistent
inode allocation performance as filesystems age.
By default, mkfs.xfs will create free inode btrees for filesystems created with the (default) -m
crc=1 option set. When the option -m crc=0 is used, the free inode btree feature is not supported
and is disabled.
uuid=value
Use the given value as the filesystem UUID for the newly created filesystem. The default is to
generate a random UUID.
rmapbt=value
This option enables the creation of a reverse-mapping btree index in each allocation group. The
value is either 0 to disable the feature, or 1 to create the btree.
The reverse mapping btree maps filesystem blocks to the owner of the filesystem block. Most of the
mappings will be to an inode number and an offset, though there will also be mappings to filesystem
metadata. This secondary metadata can be used to validate the primary metadata or to pinpoint
exactly which data has been lost when a disk error occurs.
By default, mkfs.xfs will not create reverse mapping btrees. This feature is only available for
filesystems created with the (default) -m crc=1 option set. When the option -m crc=0 is used, the
reverse mapping btree feature is not supported and is disabled.
reflink=value
This option enables the use of a separate reference count btree index in each allocation group. The
value is either 0 to disable the feature, or 1 to create a reference count btree in each allocation
group.
The reference count btree enables the sharing of physical extents between the data forks of differ‐
ent files, which is commonly known as "reflink". Unlike traditional Unix filesystems which assume
that every inode and logical block pair map to a unique physical block, a reflink-capable XFS
filesystem removes the uniqueness requirement, allowing up to four billion arbitrary inode/logical
block pairs to map to a physical block. If a program tries to write to a multiply-referenced block
in a file, the write will be redirected to a new block, and that file's logical-to-physical mapping
will be changed to the new block ("copy on write"). This feature enables the creation of per-file
snapshots and deduplication. It is only available for the data forks of regular files.
By default in Red Hat Enterprise Linux 8, mkfs.xfs will create reference count btrees and therefore
will enable the reflink feature. This feature is only available for filesystems created with the
(default) -m crc=1 option set. When the option -m crc=0 is used, the reference count btree feature
is not supported and reflink is disabled.
Note: the filesystem DAX mount option ( -o dax ) is incompatible with reflink-enabled XFS filesys‐
tems. To use filesystem DAX with XFS, specify the -m reflink=0 option to mkfs.xfs to disable the
reflink feature.
-d data_section_options
These options specify the location, size, and other parameters of the data section of the filesystem. The valid
data_section_options are:
agcount=value
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 allocating 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).
agsize=value
This is an alternative to using the agcount suboption. The value is the desired size of the alloca‐
tion 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 auto‐
matically adjusted to properly align with the stripe geometry. The agcount and agsize suboptions
are mutually exclusive.
cowextsize=value
Set the copy-on-write extent size hint on all inodes created by mkfs.xfs. The value must be pro‐
vided in units of filesystem blocks. If the value is zero, the default value (currently 32 blocks)
will be used. Directories will pass on this hint to newly created children.
name=value
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.
file[=value]
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.
size=value
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.
sunit=value
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.
su=value
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.
swidth=value
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.
sw=value
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 log‐
ical volume for appropriate sunit and swidth values.
noalign
This option disables automatic geometry detection and creates the filesystem without stripe geome‐
try alignment even if the underlying storage device provides this information.
rtinherit=value
If set, all inodes created by mkfs.xfs will be created with the realtime flag set. Directories
will pass on this flag to newly created children.
projinherit=value
All inodes created by mkfs.xfs will be assigned this project quota id. Directories will pass on
the project id to newly created children.
extszinherit=value
All inodes created by mkfs.xfs will have this extent size hint applied. The value must be provided
in units of filesystem blocks. Directories will pass on this hint to newly created children.
-f Force overwrite when an existing filesystem is detected on the device. By default, mkfs.xfs will not write to
the device if it suspects that there is a filesystem or partition table on the device already.
-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 inode_options are:
size=value | perblock=value
The inode size is specified either as a value in bytes with size= or as the number fitting in a
filesystem block with perblock=. The minimum (and default) value is 256 bytes without crc, 512
bytes with crc enabled. 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 num‐
ber is affected by filesystem geometry. In practice, filesystem size and inode size are the pre‐
dominant 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 sufficiently large, mkfs.xfs will warn if this
will create inode numbers > 32 significant bits.
maxpct=value
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, sub‐
ject to inode32 restrictions.
This value can be modified with xfs_growfs(8).
align[=value]
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 allo‐
cated 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).
attr=value
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 back‐
wards compatibility with kernels older than version 2.6.16.
projid32bit[=value]
This is used to enable 32bit quota project identifiers. The value is either 0 or 1, with 1 signify‐
ing that 32bit projid are to be enabled. If the value is omitted, 1 is assumed. (This default
changed in release version 3.2.0.)
sparse[=value]
Enable sparse inode chunk allocation. The value is either 0 or 1, with 1 signifying that sparse
allocation is enabled. If the value is omitted, 1 is assumed. Sparse inode allocation is disabled
by default. This feature is only available for filesystems formatted with -m crc=1.
When enabled, sparse inode allocation allows the filesystem to allocate smaller than the standard
64-inode chunk when free space is severely limited. This feature is useful for filesystems that
might fragment free space over time such that no free extents are large enough to accommodate a
chunk of 64 inodes. Without this feature enabled, inode allocations can fail with out of space
errors under severe fragmented free space conditions.
-l log_section_options
These options specify the location, size, and other parameters of the log section of the filesystem. The valid
log_section_options are:
agnum=value
If the log is internal, allocate it in this AG.
internal[=value]
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.
logdev=device
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.
size=value
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 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 value is specified in bytes or blocks, with a b
suffix meaning multiplication by the filesystem block size, as described above. The overriding min‐
imum value for size is 512 blocks. With some combinations of filesystem block size, inode size,
and directory block size, the minimum log size is larger than 512 blocks.
version=value
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.
sunit=value
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 per‐
formance on some configurations such as software RAID5 when the sunit is specified as the filesys‐
tem 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.
su=value
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.
lazy-count=value
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 serialization 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 coun‐
ters. 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 signifi‐
cant 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 support it
-n naming_options
These options specify the version and size parameters for the naming (directory) area of the filesystem. The
valid naming_options are:
size=value
The directory block size is specified with a value in bytes. 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 directo‐
ries 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.
version=value
The naming (directory) version value can be either 2 or 'ci', defaulting to 2 if unspecified. With
version 2 directories, 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 directo‐
ries. 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.
ftype=value
This feature allows the inode type to be stored in the directory structure so that the readdir(3)
and getdents(2) do not need to look up the inode to determine the inode type.
The value is either 0 or 1, with 1 signifying that filetype information will be stored in the
directory structure. The default value is 1.
When CRCs are enabled (the default), the ftype functionality is always enabled, and cannot be
turned off.
-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 com‐
patibility, 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 syntax but are meant to help you in the
following discussion of the file contents.
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 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 are ignored.
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 contains 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 charac‐
ters 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 sec‐
ond 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 sup‐
presses this.
-r realtime_section_options
These options specify the location, size, and other parameters of the real-time section of the filesystem. The
valid realtime_section_options are:
rtdev=device
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.
extsize=value
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.
size=value
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 log‐
ical volume containing the section.
noalign
This option disables stripe size detection, enforcing a realtime device with no stripe geometry.
-s sector_size_options
This option specifies the fundamental sector size of the filesystem. The valid sector_size_option is:
size=value
The sector size is specified with a value in bytes. The default sector_size is 512 bytes. The min‐
imum 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 size.
To specify any options on the command line in units of sectors, this option must be specified first
so that the sector size is applied consistently to all options.
-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 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.
-V Prints the version number and exits.
