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| <chapter id="xfs-mount"> |
| <title>mount</title> |
| <section> |
| <title>Mounting XFS Filesystems</title> |
| <para>This section describes some XFS-specific mount options and how they affect the behaviour of XFS</para> |
| </section> |
| <section> |
| <title>Mount Options</title> |
| <para>Described in</para> |
| <itemizedlist> |
| <listitem><para>In linux tree: |
| <itemizedlist> |
| <listitem><para>Documentation/filesystems/xfs.txt</para></listitem> |
| <listitem><para>xfs/fs/xfs_vfsops.c</para></listitem> |
| </itemizedlist> |
| </para></listitem> |
| <listitem><para><command>mount(8)</command></para></listitem> |
| </itemizedlist> |
| <para>What options are specific to XFS?</para> |
| <para>What common Linux mount options does XFS not support?</para> |
| </section> |
| <section> |
| <title>Mount Options - Log & Realtime Devices</title> |
| <para>Use an external log (metadata journal) device:</para> |
| <para><command>mount -o logdev=<replaceable>log_device</replaceable> <replaceable>device</replaceable> <replaceable>mountpoint</replaceable></command></para> |
| <para>Use an external log (metadata journal) and real-time device:</para> |
| <para><command>mount -o logdev=<replaceable>log_device</replaceable>,rtdev=<replaceable>rt_device</replaceable> <replaceable>device</replaceable> <replaceable>mountpoint</replaceable></command></para> |
| </section> |
| <section> |
| <title>Mount Options - 32 or 64 bit Inodes</title> |
| <para>The inode's number is derived from its location on disk |
| <itemizedlist> |
| <listitem><para>Combination of allocation group, cluster and block</para></listitem> |
| </itemizedlist> |
| </para> |
| <para>32 bit inodes (default):</para> |
| <itemizedlist> |
| <listitem><para>Allocator can only place 32bit inodes in the first terabyte |
| <itemizedlist> |
| <listitem><para>Using a larger inode size means less inodes per cluster allowing 32bit |
| inodes to be located beyond the first terabyte</para></listitem> |
| </itemizedlist> |
| </para></listitem> |
| <listitem><para>Allocator will rotate data extents across allocations groups to leave room for inodes</para></listitem> |
| </itemizedlist> |
| |
| <para>64 bit inodes:</para> |
| <itemizedlist> |
| <listitem><para>Only available on 64bit machines</para></listitem> |
| <listitem><para>Use inode64 mount option to enable</para></listitem> |
| <listitem><para>Allows inodes to span the entire filesystem</para></listitem> |
| <listitem><para>Allocator will try to put file extents in same allocation group as inode</para></listitem> |
| <listitem><para>Not all backup tools support 64bit inodes |
| <itemizedlist> |
| <listitem><para>Inode number used to uniquely identify files in backups</para></listitem> |
| </itemizedlist> |
| </para></listitem> |
| </itemizedlist> |
| </section> |
| <section> |
| <title>Mount Options - Stripes</title> |
| <para>Specify the stripe unit and width for a RAID device or a stripe volume.</para> |
| <para>Values must be specified in 512-byte block units.</para> |
| <para>For example, to use a stripe unit of 1MB and a stripe width of 8MB:</para> |
| <para><command>mount -o sunit=2048,swidth=16384 <replaceable>device</replaceable> <replaceable>mountpoint</replaceable></command></para> |
| <para><command>swalloc</command> mount option</para> |
| <itemizedlist> |
| <listitem><para>data allocations will be rounded up to stripe width boundaries when the |
| current end of file is being extended and the file size is larger than the |
| stripe width size.</para></listitem> |
| </itemizedlist> |
| </section> |
| <section> |
| <title>Mount Options - Large I/O</title> |
| <para>These mount options affect the preferred filesystem I/O size reported by <command>stat(2)</command></para> |
| <para><command>largeio</command></para> |
| <itemizedlist> |
| <listitem><para>A filesystem that has a <command>swidth</command> specified will return the |
| <command>swidth</command> value (in bytes) in st_blksize</para></listitem> |
| <listitem><para>If the filesystem does not have a <command>swidth</command> specified but does |
| specify an <command>allocsize</command> then <command>allocsize</command> |
| (in bytes) will be returned instead.</para></listitem> |
| </itemizedlist> |
| <para><command>nolargeio</command> (default)</para> |
| <itemizedlist> |
| <listitem><para>The optimal I/O reported in st_blksize will be as small as possible to |
| allow user applications to avoid inefficient read/modify/write I/O.</para></listitem> |
| </itemizedlist> |
| <para>If neither of these two options are specified, then the filesystem will behave as if |
| <command>nolargeio</command> was specified.</para> |
| </section> |
| <section> |
| <title>Mount Options - Performance Tweaks</title> |
| <para><command>osyncisdsync</command> (default/deprecated)</para> |
| <itemizedlist> |
| <listitem><para>Writes to files opened with the O_SYNC flag set will behave as if the O_DSYNC |
| flag had been used instead.</para></listitem> |
| <listitem><para>This can result in better performance without compromising data safety.</para></listitem> |
| <listitem><para>However timestamp updates from O_SYNC writes can be lost if the system crashes. |
| Use <command>osyncisosync</command> to disable this setting.</para></listitem> |
| </itemizedlist> |
| <para><command>ikeep</command></para> |
| <itemizedlist> |
| <listitem><para>When inode clusters are emptied of inodes, keep them around on the disk.</para></listitem> |
| <listitem><para>Use the <command>noikeep</command> option to force empty inode clusters to be returned to |
| the free space pool.</para></listitem> |
| </itemizedlist> |
| </section> |
| <section> |
| <title>Mount Options - Extended Attributes</title> |
| <para><command>attr2 (default)</command></para> |
| <itemizedlist> |
| <listitem><para>Enable the use of version two of the extended attribute inline allocation policy.</para></listitem> |
| </itemizedlist> |
| <para><command>noattr2</command></para> |
| <itemizedlist> |
| <listitem><para>Force the use of version one of the extended attribute inline allocation policy.</para></listitem> |
| </itemizedlist> |
| <para>When the new form is used for the first time (by setting or removing extended attributes) |
| the on-disk superblock feature bit field will be updated to reflect this format being in use.</para> |
| <para><command>mount -o attr2 <replaceable>device</replaceable> <replaceable>mountpoint</replaceable></command></para> |
| </section> |
| <section> |
| <title>Mount Options - Group Ids</title> |
| <para>These options define what group ID a newly created file gets.</para> |
| <para><command>grpid/bsdgroups</command></para> |
| <itemizedlist> |
| <listitem><para>Take the group ID of the directory in which it is created</para></listitem> |
| </itemizedlist> |
| <para><command>nogrpid/sysvgroups</command></para> |
| <itemizedlist> |
| <listitem><para>Take the fsgid of the current process, unless the directory has the setgid bit |
| set, in which case it takes the gid from the parent directory, and also gets the |
| setgid bit set if it is a directory itself.</para></listitem> |
| </itemizedlist> |
| </section> |
| <section> |
| <title>Mount Options - Recovery</title> |
| <para>An XFS filesystem can be mounted without running log recovery.</para> |
| <para>If the filesystem was not cleanly unmounted, it is likely to be inconsistent when mounted |
| in <command>norecovery</command> mode. Some files or directories may not be accessible because of this.</para> |
| <para>Filesystems mounted <command>norecovery</command> must be mounted read-only or the mount will fail.</para> |
| <para><command>mount -o ro,norecovery <replaceable>device</replaceable> <replaceable>mountpoint</replaceable></command></para> |
| </section> |
| <section> |
| <title>Mount Options - Barriers</title> |
| <para>Write caches on disks can result in filesystem corruption since XFS may be told a |
| log transaction has reached the disk when in fact it is still in the disk cache.</para> |
| <itemizedlist> |
| <listitem><para>A journal log assumes that the log transaction is updated on disk before |
| updating the metadata in the filesystem, but this may not be true with |
| write caching</para></listitem> |
| </itemizedlist> |
| <para>XFS is able to issue write barriers if the underlying devices support it</para> |
| <itemizedlist> |
| <listitem><para>Ensures that the log entry is written before any other data</para></listitem> |
| </itemizedlist> |
| <para>Write barriers are enabled by default in XFS</para> |
| <itemizedlist> |
| <listitem><para>Filesystem will attempt to determine if barriers are supported and will |
| issue a warning to the syslog if they are not</para></listitem> |
| <listitem><para>The <command>nobarrier</command> option disables write barriers</para></listitem> |
| <listitem><para>Barriers should be disabled when using a RAID with battery backed controller |
| cache (but only if the individual disk write caches are disabled)</para></listitem> |
| </itemizedlist> |
| <para>See</para> |
| <itemizedlist> |
| <listitem><para><ulink |
| url="http://xfs.org/index.php/XFS_FAQ#Q:_What_is_the_problem_with_the_write_cache_on_journaled_filesystems.3F">http://xfs.org/index.php/XFS_FAQ#Q:_What_is_the_problem_with_the_write_cache_on_journaled_filesystems.3F</ulink></para></listitem> |
| </itemizedlist> |
| </section> |
| <section> |
| <title>Mount Options - User/Group/Project Quotas</title> |
| <para>User disk quota accounting enabled, and limits (optionally) enforced.</para> |
| <para><command>mount -o uquota <replaceable>device</replaceable> <replaceable>mountpoint</replaceable></command></para> |
| <para>Group disk quota accounting enabled, and limits (optionally) enforced.</para> |
| <para><command>mount -o grpquota <replaceable>device</replaceable> <replaceable>mountpoint</replaceable></command></para> |
| <para>Project quota accounting enabled, and limits (optionally) enforced.</para> |
| <para><command>mount -o prjquota <replaceable>device</replaceable> <replaceable>mountpoint</replaceable></command></para> |
| <para>Can optionally specify <command>uqnoenforce</command>, |
| <command>gqnoenforce</command> and <command>pqnoenforce</command> |
| to use soft limits.</para> |
| </section> |
| </chapter> |
