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 Enables/disables the use of block layer write barriers for
105 writes into the journal and for data integrity operations. This
106 allows for drive level write caching to be enabled, for devices
107 that support write barriers.
108 Barriers are enabled by default.
110 discard|nodiscard
112 Enable/disable the issuing of commands to let the block device
113 reclaim space freed by the filesystem. This is useful for SSD
114 devices, thinly provisioned LUNs and virtual machine images, but
115 may have a performance impact.
116 Note: It is currently recommended that you use the fstrim appli‐
118 cation to discard unused blocks rather than the discard mount
119 option because the performance impact of this option is quite
120 severe. For this reason, nodiscard is the default.
121 grpid|bsdgroups|nogrpid|sysvgroups
123 These options define what group ID a newly created file gets.
124 When grpid is set, it takes the group ID of the directory in
125 which it is created; otherwise it takes the fsgid of the current
126 process, unless the directory has the setgid bit set, in which
127 case it takes the gid from the parent directory, and also gets
128 the setgid bit set if it is a directory itself.
129 filestreams
131 Make the data allocator use the filestreams allocation mode
132 across the entire filesystem rather than just on directories
133 configured to use it.
134 ikeep|noikeep
136 When ikeep is specified, XFS does not delete empty inode clus‐
137 ters and keeps them around on disk. When noikeep is specified,
138 empty inode clusters are returned to the free space pool.
139 noikeep is the default.
140 inode32|inode64
142 When inode32 is specified, it indicates that XFS limits inode
143 creation to locations which will not result in inode numbers
144 with more than 32 bits of significance.
145 When inode64 is specified, it indicates that XFS is allowed to
147 create inodes at any location in the filesystem, including those
148 which will result in inode numbers occupying more than 32 bits
149 of significance.
150 inode32 is provided for backwards compatibility with older sys‐
152 tems and applications, since 64 bits inode numbers might cause
153 problems for some applications that cannot handle large inode
154 numbers. If applications are in use which do not handle inode
155 numbers bigger than 32 bits, the inode32 option should be speci‐
156 fied.
157 For kernel v3.7 and later, inode64 is the default.
159 largeio|nolargeio
161 If "nolargeio" is specified, the optimal I/O reported in st_blk‐
162 size by stat(2) will be as small as possible to allow user
163 applications to avoid inefficient read/modify/write I/O. This
164 is typically the page size of the machine, as this is the granu‐
165 larity of the page cache.
166 If "largeio" specified, a filesystem that was created with a
168 "swidth" specified will return the "swidth" value (in bytes) in
169 st_blksize. If the filesystem does not have a "swidth" specified
170 but does specify an "allocsize" then "allocsize" (in bytes) will
171 be returned instead. Otherwise the behavior is the same as if
172 "nolargeio" was specified. nolargeio is the default.
173 logbufs=value
175 Set the number of in-memory log buffers. Valid numbers range
176 from 2–8 inclusive.
177 The default value is 8 buffers.
179 If the memory cost of 8 log buffers is too high on small sys‐
181 tems, then it may be reduced at some cost to performance on
182 metadata intensive workloads. The logbsize option below controls
183 the size of each buffer and so is also relevant to this case.
184 logbsize=value
186 Set the size of each in-memory log buffer. The size may be
187 specified in bytes, or in kibibytes (KiB) with a "k" suffix.
188 Valid sizes for version 1 and version 2 logs are 16384
189 (value=16k) and 32768 (value=32k). Valid sizes for version 2
190 logs also include 65536 (value=64k), 131072 (value=128k) and
191 262144 (value=256k). The logbsize must be an integer multiple of
192 the log stripe unit configured at mkfs time.
193 The default value for version 1 logs is 32768, while the default
195 value for version 2 logs is MAX(32768, log_sunit).
196 logdev=device and rtdev=device
198 Use an external log (metadata journal) and/or real-time device.
199 An XFS filesystem has up to three parts: a data section, a log
200 section, and a real-time section. The real-time section is
201 optional, and the log section can be separate from the data sec‐
202 tion or contained within it.
203 noalign
205 Data allocations will not be aligned at stripe unit boundaries.
206 This is only relevant to filesystems created with non-zero data
207 alignment parameters (sunit, swidth) by mkfs.
208 norecovery
210 The filesystem will be mounted without running log recovery. If
211 the filesystem was not cleanly unmounted, it is likely to be
212 inconsistent when mounted in "norecovery" mode. Some files or
213 directories may not be accessible because of this. Filesystems
214 mounted "norecovery" must be mounted read-only or the mount will
215 fail.
216 nouuid Don't check for double mounted file systems using the file sys‐
218 tem uuid. This is useful to mount LVM snapshot volumes, and
219 often used in combination with "norecovery" for mounting read-
220 only snapshots.
221 noquota
223 Forcibly turns off all quota accounting and enforcement within
224 the filesystem.
225 uquota/usrquota/quota/uqnoenforce/qnoenforce
227 User disk quota accounting enabled, and limits (optionally)
228 enforced. Refer to xfs_quota(8) for further details.
229 gquota/grpquota/gqnoenforce
231 Group disk quota accounting enabled and limits (optionally)
232 enforced. Refer to xfs_quota(8) for further details.
233 pquota/prjquota/pqnoenforce
235 Project disk quota accounting enabled and limits (optionally)
236 enforced. Refer to xfs_quota(8) for further details.
237 sunit=value and swidth=value
239 Used to specify the stripe unit and width for a RAID device or a
240 stripe volume. "value" must be specified in 512-byte block
241 units. These options are only relevant to filesystems that were
242 created with non-zero data alignment parameters.
243 The sunit and swidth parameters specified must be compatible
245 with the existing filesystem alignment characteristics. In gen‐
246 eral, that means the only valid changes to sunit are increasing
247 it by a power-of-2 multiple. Valid swidth values are any integer
248 multiple of a valid sunit value.
249 Typically the only time these mount options are necessary if
251 after an underlying RAID device has had it's geometry modified,
252 such as adding a new disk to a RAID5 lun and reshaping it.
253 swalloc
255 Data allocations will be rounded up to stripe width boundaries
256 when the current end of file is being extended and the file size
257 is larger than the stripe width size.
258 wsync When specified, all filesystem namespace operations are executed
260 synchronously. This ensures that when the namespace operation
261 (create, unlink, etc) completes, the change to the namespace is
262 on stable storage. This is useful in HA setups where failover
263 must not result in clients seeing inconsistent namespace presen‐
264 tation during or after a failover event.
265
267 The XFS filesystem supports setting the following file attributes on
268 Linux systems using the chattr(1) utility:
269 a - append only
271 A - no atime updates
273 d - no dump
275 i - immutable
277 S - synchronous updates
279 For descriptions of these attribute flags, please refer to the
281 chattr(1) man page.
282
284 chattr(1), xfsctl(3), mount(8), mkfs.xfs(8), xfs_info(8), xfs_admin(8),
285 xfsdump(8), xfsrestore(8).
286 xfs(5)