1xfs(5) File Formats Manual xfs(5)
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6 xfs - layout, mount options, and supported file attributes for the XFS
7 filesystem
8
10 An XFS filesystem can reside on a regular disk partition or on a logi‐
11 cal volume. An XFS filesystem has up to three parts: a data section, a
12 log section, and a realtime section. Using the default mkfs.xfs(8)
13 options, the realtime section is absent, and the log area is contained
14 within the data section. The log section can be either separate from
15 the data section or contained within it. The filesystem sections are
16 divided into a certain number of blocks, whose size is specified at
17 mkfs.xfs(8) time with the -b option.
18 The data section contains all the filesystem metadata (inodes, directo‐
20 ries, indirect blocks) as well as the user file data for ordinary (non-
21 realtime) files and the log area if the log is internal to the data
22 section. The data section is divided into a number of allocation
23 groups. The number and size of the allocation groups are chosen by
24 mkfs.xfs(8) so that there is normally a small number of equal-sized
25 groups. The number of allocation groups controls the amount of paral‐
26 lelism available in file and block allocation. It should be increased
27 from the default if there is sufficient memory and a lot of allocation
28 activity. The number of allocation groups should not be set very high,
29 since this can cause large amounts of CPU time to be used by the
30 filesystem, especially when the filesystem is nearly full. More allo‐
31 cation groups are added (of the original size) when xfs_growfs(8) is
32 run.
33 The log section (or area, if it is internal to the data section) is
35 used to store changes to filesystem metadata while the filesystem is
36 running until those changes are made to the data section. It is writ‐
37 ten sequentially during normal operation and read only during mount.
38 When mounting a filesystem after a crash, the log is read to complete
39 operations that were in progress at the time of the crash.
40 The realtime section is used to store the data of realtime files.
42 These files had an attribute bit set through xfsctl(3) after file cre‐
43 ation, before any data was written to the file. The realtime section
44 is divided into a number of extents of fixed size (specified at
45 mkfs.xfs(8) time). Each file in the realtime section has an extent
46 size that is a multiple of the realtime section extent size.
47 Each allocation group contains several data structures. The first sec‐
49 tor contains the superblock. For allocation groups after the first,
50 the superblock is just a copy and is not updated after mkfs.xfs(8).
51 The next three sectors contain information for block and inode alloca‐
52 tion within the allocation group. Also contained within each alloca‐
53 tion group are data structures to locate free blocks and inodes; these
54 are located through the header structures.
55 Each XFS filesystem is labeled with a Universal Unique Identifier
57 (UUID). The UUID is stored in every allocation group header and is
58 used to help distinguish one XFS filesystem from another, therefore you
59 should avoid using dd(1) or other block-by-block copying programs to
60 copy XFS filesystems. If two XFS filesystems on the same machine have
61 the same UUID, xfsdump(8) may become confused when doing incremental
62 and resumed dumps. xfsdump(8) and xfsrestore(8) are recommended for
63 making copies of XFS filesystems.
64
66 Some functionality specific to the XFS filesystem is accessible to
67 applications through the xfsctl(3) and by-handle (see open_by_han‐
68 dle(3)) interfaces.
69
71 The following XFS-specific mount options may be used when mounting an
72 XFS filesystem. Other generic options may be used as well; refer to the
73 mount(8) manual page for more details.
74 allocsize=size
76 Sets the buffered I/O end-of-file preallocation size when doing
77 delayed allocation writeout. Valid values for this option are
78 page size (typically 4KiB) through to 1GiB, inclusive, in power-
79 of-2 increments.
80 The default behavior is for dynamic end-of-file preallocation
82 size, which uses a set of heuristics to optimise the prealloca‐
83 tion size based on the current allocation patterns within the
84 file and the access patterns to the file. Specifying a fixed
85 allocsize value turns off the dynamic behavior.
86 attr2|noattr2
88 The options enable/disable an "opportunistic" improvement to be
89 made in the way inline extended attributes are stored on-disk.
90 When the new form is used for the first time when attr2 is
91 selected (either when setting or removing extended attributes)
92 the on-disk superblock feature bit field will be updated to
93 reflect this format being in use.
94 The default behavior is determined by the on-disk feature bit
96 indicating that attr2 behavior is active. If either mount option
97 it set, then that becomes the new default used by the filesys‐
98 tem.
99 CRC enabled filesystems always use the attr2 format, and so will
101 reject the noattr2 mount option if it is set.
102 barrier|nobarrier
104 Note: This option has been deprecated as of kernel v4.10; in
105 that version, integrity operations are always performed and the
106 mount option is ignored. These mount options will be removed no
107 earlier than kernel v4.15.
108 Enables/disables the use of block layer write barriers for
110 writes into the journal and for data integrity operations. This
111 allows for drive level write caching to be enabled, for devices
112 that support write barriers.
113 Barriers are enabled by default.
115 discard|nodiscard
117 Enable/disable the issuing of commands to let the block device
118 reclaim space freed by the filesystem. This is useful for SSD
119 devices, thinly provisioned LUNs and virtual machine images, but
120 may have a performance impact.
121 Note: It is currently recommended that you use the fstrim appli‐
123 cation to discard unused blocks rather than the discard mount
124 option because the performance impact of this option is quite
125 severe. For this reason, nodiscard is the default.
126 grpid|bsdgroups|nogrpid|sysvgroups
128 These options define what group ID a newly created file gets.
129 When grpid is set, it takes the group ID of the directory in
130 which it is created; otherwise it takes the fsgid of the current
131 process, unless the directory has the setgid bit set, in which
132 case it takes the gid from the parent directory, and also gets
133 the setgid bit set if it is a directory itself.
134 filestreams
136 Make the data allocator use the filestreams allocation mode
137 across the entire filesystem rather than just on directories
138 configured to use it.
139 ikeep|noikeep
141 When ikeep is specified, XFS does not delete empty inode clus‐
142 ters and keeps them around on disk. When noikeep is specified,
143 empty inode clusters are returned to the free space pool.
144 noikeep is the default.
145 inode32|inode64
147 When inode32 is specified, it indicates that XFS limits inode
148 creation to locations which will not result in inode numbers
149 with more than 32 bits of significance.
150 When inode64 is specified, it indicates that XFS is allowed to
152 create inodes at any location in the filesystem, including those
153 which will result in inode numbers occupying more than 32 bits
154 of significance.
155 inode32 is provided for backwards compatibility with older sys‐
157 tems and applications, since 64 bits inode numbers might cause
158 problems for some applications that cannot handle large inode
159 numbers. If applications are in use which do not handle inode
160 numbers bigger than 32 bits, the inode32 option should be speci‐
161 fied.
162 For kernel v3.7 and later, inode64 is the default.
164 largeio|nolargeio
166 If "nolargeio" is specified, the optimal I/O reported in st_blk‐
167 size by stat(2) will be as small as possible to allow user
168 applications to avoid inefficient read/modify/write I/O. This
169 is typically the page size of the machine, as this is the granu‐
170 larity of the page cache.
171 If "largeio" specified, a filesystem that was created with a
173 "swidth" specified will return the "swidth" value (in bytes) in
174 st_blksize. If the filesystem does not have a "swidth" specified
175 but does specify an "allocsize" then "allocsize" (in bytes) will
176 be returned instead. Otherwise the behavior is the same as if
177 "nolargeio" was specified. nolargeio is the default.
178 logbufs=value
180 Set the number of in-memory log buffers. Valid numbers range
181 from 2–8 inclusive.
182 The default value is 8 buffers.
184 If the memory cost of 8 log buffers is too high on small sys‐
186 tems, then it may be reduced at some cost to performance on
187 metadata intensive workloads. The logbsize option below controls
188 the size of each buffer and so is also relevant to this case.
189 logbsize=value
191 Set the size of each in-memory log buffer. The size may be
192 specified in bytes, or in kibibytes (KiB) with a "k" suffix.
193 Valid sizes for version 1 and version 2 logs are 16384
194 (value=16k) and 32768 (value=32k). Valid sizes for version 2
195 logs also include 65536 (value=64k), 131072 (value=128k) and
196 262144 (value=256k). The logbsize must be an integer multiple of
197 the log stripe unit configured at mkfs time.
198 The default value for version 1 logs is 32768, while the default
200 value for version 2 logs is MAX(32768, log_sunit).
201 logdev=device and rtdev=device
203 Use an external log (metadata journal) and/or real-time device.
204 An XFS filesystem has up to three parts: a data section, a log
205 section, and a real-time section. The real-time section is
206 optional, and the log section can be separate from the data sec‐
207 tion or contained within it.
208 noalign
210 Data allocations will not be aligned at stripe unit boundaries.
211 This is only relevant to filesystems created with non-zero data
212 alignment parameters (sunit, swidth) by mkfs.
213 norecovery
215 The filesystem will be mounted without running log recovery. If
216 the filesystem was not cleanly unmounted, it is likely to be
217 inconsistent when mounted in "norecovery" mode. Some files or
218 directories may not be accessible because of this. Filesystems
219 mounted "norecovery" must be mounted read-only or the mount will
220 fail.
221 nouuid Don't check for double mounted file systems using the file sys‐
223 tem uuid. This is useful to mount LVM snapshot volumes, and
224 often used in combination with "norecovery" for mounting read-
225 only snapshots.
226 noquota
228 Forcibly turns off all quota accounting and enforcement within
229 the filesystem.
230 uquota/usrquota/quota/uqnoenforce/qnoenforce
232 User disk quota accounting enabled, and limits (optionally)
233 enforced. Refer to xfs_quota(8) for further details.
234 gquota/grpquota/gqnoenforce
236 Group disk quota accounting enabled and limits (optionally)
237 enforced. Refer to xfs_quota(8) for further details.
238 pquota/prjquota/pqnoenforce
240 Project disk quota accounting enabled and limits (optionally)
241 enforced. Refer to xfs_quota(8) for further details.
242 sunit=value and swidth=value
244 Used to specify the stripe unit and width for a RAID device or a
245 stripe volume. "value" must be specified in 512-byte block
246 units. These options are only relevant to filesystems that were
247 created with non-zero data alignment parameters.
248 The sunit and swidth parameters specified must be compatible
250 with the existing filesystem alignment characteristics. In gen‐
251 eral, that means the only valid changes to sunit are increasing
252 it by a power-of-2 multiple. Valid swidth values are any integer
253 multiple of a valid sunit value.
254 Typically the only time these mount options are necessary if
256 after an underlying RAID device has had it's geometry modified,
257 such as adding a new disk to a RAID5 lun and reshaping it.
258 swalloc
260 Data allocations will be rounded up to stripe width boundaries
261 when the current end of file is being extended and the file size
262 is larger than the stripe width size.
263 wsync When specified, all filesystem namespace operations are executed
265 synchronously. This ensures that when the namespace operation
266 (create, unlink, etc) completes, the change to the namespace is
267 on stable storage. This is useful in HA setups where failover
268 must not result in clients seeing inconsistent namespace presen‐
269 tation during or after a failover event.
270
272 The XFS filesystem supports setting the following file attributes on
273 Linux systems using the chattr(1) utility:
274 a - append only
276 A - no atime updates
278 d - no dump
280 i - immutable
282 S - synchronous updates
284 For descriptions of these attribute flags, please refer to the
286 chattr(1) man page.
287
289 chattr(1), xfsctl(3), mount(8), mkfs.xfs(8), xfs_info(8), xfs_admin(8),
290 xfsdump(8), xfsrestore(8).
291 xfs(5)