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mkfs.xfs(8) System Manager's Manual mkfs.xfs(8)
NAME
mkfs.xfs - construct an XFS filesystem
SYNOPSIS
mkfs.xfs [ -b block_size ] [ -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 ] [ -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 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:
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 option elements in the argument list above can be given as multiple comma-sep-
arated 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 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).
OPTIONS
-b block_size_options
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). 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 are:
crc=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 depen-
dent 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 not create free inode btrees for filesystems.
This is for backwards compatibility with older RHEL7 kernels. If the
free inode btree is enabled, older RHEL7 kernels will not be able to
mount the created filesystem. 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.
-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 sec-
tion 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 alloca-
tion 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 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.
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 cur-
rent 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 suf-
fixes). 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 vol-
ume. The value is expressed as a multiplier of the stripe unit, usually
the same as the number of stripe members in the logical volume configu-
ration, 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 appropriate sunit and swidth
values.
noalign
This option disables automatic geometry detection and creates the
filesystem without stripe geometry alignment even if the underlying
storage device provides this information.
-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: direc-
tory data, for small directories; attribute data, for small attribute sets; sym-
bolic 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 number fitting in a
filesystem block with perblock=. The minimum (and default) value is
256 bytes. The maximum value is 2048 (2 KiB) subject to the restric-
tion that the inode size cannot exceed one half of the filesystem block
size.
XFS uses 64-bit inode numbers internally; however, the number of sig-
nificant bits in an inode number is affected by filesystem geometry.
In practice, filesystem size and inode size are the predominant fac-
tors. The Linux kernel (on 32 bit hardware platforms) and most appli-
cations cannot currently handle inode numbers greater than 32 signifi-
cant 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 suffi-
ciently 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 signifi-
cant 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 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 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).
attr=value
This is used to specify the version of extended attribute inline allo-
cation policy to be used. By default, this is 2, which uses an effi-
cient 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.
projid32bit[=value]
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, 1 is assumed. (This default changed in
release version 3.2.0.)
sparse[=value]
Enable sparse inode chunk allocation. This experimental option is not
available in RHEL7.
-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:
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 speci-
fied, 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 mul-
tiplication by the filesystem block size, as described above. The over-
riding minimum value for size is 512 blocks. With some combinations of
filesystem block size, inode size, and directory block size, the mini-
mum 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 spec-
ify 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.
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 automati-
cally 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 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 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 | 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.
version=value
The naming (directory) version value can be either 2 or 'ci', default-
ing 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 directories. Filenames are case-preserving, that
is, the names are stored in directories using the case they were cre-
ated with.
Note: Version 1 directories are not supported.
ftype=value
This feature allows the inode type to be stored in the directory struc-
ture 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 proto-
type file and takes its directions from that file. The blocks and inodes speci-
fiers 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 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 immate-
rial 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 com-
mand 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 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 recur-
sive 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 con-
structed; the -q flag suppresses 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 subop-
tion is only needed if the real-time section of the filesystem should
occupy less space than the size of the partition or logical volume con-
taining the section.
noalign
This option disables stripe size detection, enforcing a realtime device
with no stripe geometry.
-s sector_size
This option specifies the fundamental sector size of the filesystem. The sec-
tor_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 size.
-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.
SEE ALSO
xfs(5), mkfs(8), mount(8), xfs_info(8), xfs_admin(8).
BUGS
With a prototype file, it is not possible to specify hard links.
mkfs.xfs(8)
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