docs: make ext4 readme tables readable
The tables in the ext4 readme are not particularly space efficient in the text or html outputs, and they're totally broken in the pdf output. Convert them into titled paragraphs so that they render more nicely. Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com> Signed-off-by: Theodore Ts'o <tytso@mit.edu>
This commit is contained in:
Darrick J. Wong
Theodore Ts'o
parent
de7abd7bbb
commit
c0e3e0406a
@ -101,269 +101,256 @@ Options
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When mounting an ext4 filesystem, the following option are accepted:
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(*) == default
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======================= =======================================================
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Mount Option Description
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======================= =======================================================
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ro Mount filesystem read only. Note that ext4 will
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replay the journal (and thus write to the
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partition) even when mounted "read only". The
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mount options "ro,noload" can be used to prevent
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writes to the filesystem.
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ro
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Mount filesystem read only. Note that ext4 will replay the journal (and
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thus write to the partition) even when mounted "read only". The mount
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options "ro,noload" can be used to prevent writes to the filesystem.
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journal_checksum Enable checksumming of the journal transactions.
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This will allow the recovery code in e2fsck and the
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kernel to detect corruption in the kernel. It is a
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compatible change and will be ignored by older kernels.
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journal_checksum
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Enable checksumming of the journal transactions. This will allow the
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recovery code in e2fsck and the kernel to detect corruption in the
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kernel. It is a compatible change and will be ignored by older
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kernels.
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journal_async_commit Commit block can be written to disk without waiting
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for descriptor blocks. If enabled older kernels cannot
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mount the device. This will enable 'journal_checksum'
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internally.
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journal_async_commit
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Commit block can be written to disk without waiting for descriptor
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blocks. If enabled older kernels cannot mount the device. This will
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enable 'journal_checksum' internally.
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journal_path=path
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journal_dev=devnum When the external journal device's major/minor numbers
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have changed, these options allow the user to specify
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the new journal location. The journal device is
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identified through either its new major/minor numbers
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encoded in devnum, or via a path to the device.
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journal_path=path, journal_dev=devnum
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When the external journal device's major/minor numbers have changed,
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these options allow the user to specify the new journal location. The
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journal device is identified through either its new major/minor numbers
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encoded in devnum, or via a path to the device.
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norecovery Don't load the journal on mounting. Note that
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noload if the filesystem was not unmounted cleanly,
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skipping the journal replay will lead to the
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filesystem containing inconsistencies that can
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lead to any number of problems.
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norecovery, noload
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Don't load the journal on mounting. Note that if the filesystem was
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not unmounted cleanly, skipping the journal replay will lead to the
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filesystem containing inconsistencies that can lead to any number of
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problems.
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data=journal All data are committed into the journal prior to being
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written into the main file system. Enabling
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this mode will disable delayed allocation and
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O_DIRECT support.
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data=journal
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All data are committed into the journal prior to being written into the
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main file system. Enabling this mode will disable delayed allocation
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and O_DIRECT support.
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data=ordered (*) All data are forced directly out to the main file
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system prior to its metadata being committed to the
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journal.
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data=ordered (*)
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All data are forced directly out to the main file system prior to its
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metadata being committed to the journal.
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data=writeback Data ordering is not preserved, data may be written
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into the main file system after its metadata has been
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committed to the journal.
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data=writeback
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Data ordering is not preserved, data may be written into the main file
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system after its metadata has been committed to the journal.
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commit=nrsec (*) Ext4 can be told to sync all its data and metadata
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every 'nrsec' seconds. The default value is 5 seconds.
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This means that if you lose your power, you will lose
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as much as the latest 5 seconds of work (your
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filesystem will not be damaged though, thanks to the
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journaling). This default value (or any low value)
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will hurt performance, but it's good for data-safety.
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Setting it to 0 will have the same effect as leaving
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it at the default (5 seconds).
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Setting it to very large values will improve
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performance.
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commit=nrsec (*)
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Ext4 can be told to sync all its data and metadata every 'nrsec'
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seconds. The default value is 5 seconds. This means that if you lose
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your power, you will lose as much as the latest 5 seconds of work (your
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filesystem will not be damaged though, thanks to the journaling). This
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default value (or any low value) will hurt performance, but it's good
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for data-safety. Setting it to 0 will have the same effect as leaving
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it at the default (5 seconds). Setting it to very large values will
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improve performance.
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barrier=<0|1(*)> This enables/disables the use of write barriers in
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barrier(*) the jbd code. barrier=0 disables, barrier=1 enables.
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nobarrier This also requires an IO stack which can support
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barriers, and if jbd gets an error on a barrier
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write, it will disable again with a warning.
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Write barriers enforce proper on-disk ordering
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of journal commits, making volatile disk write caches
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safe to use, at some performance penalty. If
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your disks are battery-backed in one way or another,
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disabling barriers may safely improve performance.
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The mount options "barrier" and "nobarrier" can
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also be used to enable or disable barriers, for
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consistency with other ext4 mount options.
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barrier=<0|1(*)>, barrier(*), nobarrier
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This enables/disables the use of write barriers in the jbd code.
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barrier=0 disables, barrier=1 enables. This also requires an IO stack
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which can support barriers, and if jbd gets an error on a barrier
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write, it will disable again with a warning. Write barriers enforce
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proper on-disk ordering of journal commits, making volatile disk write
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caches safe to use, at some performance penalty. If your disks are
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battery-backed in one way or another, disabling barriers may safely
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improve performance. The mount options "barrier" and "nobarrier" can
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also be used to enable or disable barriers, for consistency with other
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ext4 mount options.
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inode_readahead_blks=n This tuning parameter controls the maximum
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number of inode table blocks that ext4's inode
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table readahead algorithm will pre-read into
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the buffer cache. The default value is 32 blocks.
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inode_readahead_blks=n
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This tuning parameter controls the maximum number of inode table blocks
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that ext4's inode table readahead algorithm will pre-read into the
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buffer cache. The default value is 32 blocks.
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nouser_xattr Disables Extended User Attributes. See the
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attr(5) manual page for more information about
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extended attributes.
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nouser_xattr
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Disables Extended User Attributes. See the attr(5) manual page for
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more information about extended attributes.
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noacl This option disables POSIX Access Control List
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support. If ACL support is enabled in the kernel
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configuration (CONFIG_EXT4_FS_POSIX_ACL), ACL is
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enabled by default on mount. See the acl(5) manual
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page for more information about acl.
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noacl
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This option disables POSIX Access Control List support. If ACL support
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is enabled in the kernel configuration (CONFIG_EXT4_FS_POSIX_ACL), ACL
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is enabled by default on mount. See the acl(5) manual page for more
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information about acl.
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bsddf (*) Make 'df' act like BSD.
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minixdf Make 'df' act like Minix.
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bsddf (*)
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Make 'df' act like BSD.
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debug Extra debugging information is sent to syslog.
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minixdf
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Make 'df' act like Minix.
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abort Simulate the effects of calling ext4_abort() for
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debugging purposes. This is normally used while
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remounting a filesystem which is already mounted.
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debug
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Extra debugging information is sent to syslog.
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errors=remount-ro Remount the filesystem read-only on an error.
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errors=continue Keep going on a filesystem error.
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errors=panic Panic and halt the machine if an error occurs.
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(These mount options override the errors behavior
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specified in the superblock, which can be configured
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using tune2fs)
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abort
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Simulate the effects of calling ext4_abort() for debugging purposes.
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This is normally used while remounting a filesystem which is already
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mounted.
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data_err=ignore(*) Just print an error message if an error occurs
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in a file data buffer in ordered mode.
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data_err=abort Abort the journal if an error occurs in a file
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data buffer in ordered mode.
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errors=remount-ro
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Remount the filesystem read-only on an error.
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grpid New objects have the group ID of their parent.
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bsdgroups
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errors=continue
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Keep going on a filesystem error.
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nogrpid (*) New objects have the group ID of their creator.
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sysvgroups
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errors=panic
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Panic and halt the machine if an error occurs. (These mount options
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override the errors behavior specified in the superblock, which can be
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configured using tune2fs)
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resgid=n The group ID which may use the reserved blocks.
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data_err=ignore(*)
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Just print an error message if an error occurs in a file data buffer in
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ordered mode.
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data_err=abort
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Abort the journal if an error occurs in a file data buffer in ordered
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mode.
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resuid=n The user ID which may use the reserved blocks.
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grpid | bsdgroups
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New objects have the group ID of their parent.
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sb=n Use alternate superblock at this location.
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nogrpid (*) | sysvgroups
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New objects have the group ID of their creator.
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quota These options are ignored by the filesystem. They
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noquota are used only by quota tools to recognize volumes
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grpquota where quota should be turned on. See documentation
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usrquota in the quota-tools package for more details
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(http://sourceforge.net/projects/linuxquota).
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resgid=n
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The group ID which may use the reserved blocks.
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jqfmt=<quota type> These options tell filesystem details about quota
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usrjquota=<file> so that quota information can be properly updated
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grpjquota=<file> during journal replay. They replace the above
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quota options. See documentation in the quota-tools
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package for more details
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(http://sourceforge.net/projects/linuxquota).
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resuid=n
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The user ID which may use the reserved blocks.
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stripe=n Number of filesystem blocks that mballoc will try
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to use for allocation size and alignment. For RAID5/6
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systems this should be the number of data
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disks * RAID chunk size in file system blocks.
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sb=
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Use alternate superblock at this location.
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delalloc (*) Defer block allocation until just before ext4
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writes out the block(s) in question. This
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allows ext4 to better allocation decisions
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more efficiently.
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nodelalloc Disable delayed allocation. Blocks are allocated
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when the data is copied from userspace to the
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page cache, either via the write(2) system call
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or when an mmap'ed page which was previously
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unallocated is written for the first time.
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quota, noquota, grpquota, usrquota
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These options are ignored by the filesystem. They are used only by
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quota tools to recognize volumes where quota should be turned on. See
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documentation in the quota-tools package for more details
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(http://sourceforge.net/projects/linuxquota).
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max_batch_time=usec Maximum amount of time ext4 should wait for
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additional filesystem operations to be batch
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together with a synchronous write operation.
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Since a synchronous write operation is going to
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force a commit and then a wait for the I/O
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complete, it doesn't cost much, and can be a
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huge throughput win, we wait for a small amount
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of time to see if any other transactions can
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piggyback on the synchronous write. The
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algorithm used is designed to automatically tune
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for the speed of the disk, by measuring the
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amount of time (on average) that it takes to
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finish committing a transaction. Call this time
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the "commit time". If the time that the
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transaction has been running is less than the
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commit time, ext4 will try sleeping for the
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commit time to see if other operations will join
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the transaction. The commit time is capped by
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the max_batch_time, which defaults to 15000us
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(15ms). This optimization can be turned off
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entirely by setting max_batch_time to 0.
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jqfmt=<quota type>, usrjquota=<file>, grpjquota=<file>
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These options tell filesystem details about quota so that quota
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information can be properly updated during journal replay. They replace
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the above quota options. See documentation in the quota-tools package
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for more details (http://sourceforge.net/projects/linuxquota).
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min_batch_time=usec This parameter sets the commit time (as
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described above) to be at least min_batch_time.
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It defaults to zero microseconds. Increasing
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this parameter may improve the throughput of
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multi-threaded, synchronous workloads on very
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fast disks, at the cost of increasing latency.
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stripe=n
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Number of filesystem blocks that mballoc will try to use for allocation
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size and alignment. For RAID5/6 systems this should be the number of
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data disks * RAID chunk size in file system blocks.
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journal_ioprio=prio The I/O priority (from 0 to 7, where 0 is the
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highest priority) which should be used for I/O
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operations submitted by kjournald2 during a
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commit operation. This defaults to 3, which is
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a slightly higher priority than the default I/O
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priority.
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delalloc (*)
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Defer block allocation until just before ext4 writes out the block(s)
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in question. This allows ext4 to better allocation decisions more
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efficiently.
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auto_da_alloc(*) Many broken applications don't use fsync() when
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noauto_da_alloc replacing existing files via patterns such as
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fd = open("foo.new")/write(fd,..)/close(fd)/
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rename("foo.new", "foo"), or worse yet,
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fd = open("foo", O_TRUNC)/write(fd,..)/close(fd).
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If auto_da_alloc is enabled, ext4 will detect
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the replace-via-rename and replace-via-truncate
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patterns and force that any delayed allocation
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blocks are allocated such that at the next
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journal commit, in the default data=ordered
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mode, the data blocks of the new file are forced
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to disk before the rename() operation is
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committed. This provides roughly the same level
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of guarantees as ext3, and avoids the
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"zero-length" problem that can happen when a
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system crashes before the delayed allocation
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blocks are forced to disk.
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nodelalloc
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Disable delayed allocation. Blocks are allocated when the data is
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copied from userspace to the page cache, either via the write(2) system
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call or when an mmap'ed page which was previously unallocated is
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written for the first time.
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noinit_itable Do not initialize any uninitialized inode table
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blocks in the background. This feature may be
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used by installation CD's so that the install
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process can complete as quickly as possible; the
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inode table initialization process would then be
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deferred until the next time the file system
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is unmounted.
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max_batch_time=usec
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Maximum amount of time ext4 should wait for additional filesystem
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operations to be batch together with a synchronous write operation.
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Since a synchronous write operation is going to force a commit and then
|
||||
a wait for the I/O complete, it doesn't cost much, and can be a huge
|
||||
throughput win, we wait for a small amount of time to see if any other
|
||||
transactions can piggyback on the synchronous write. The algorithm
|
||||
used is designed to automatically tune for the speed of the disk, by
|
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measuring the amount of time (on average) that it takes to finish
|
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committing a transaction. Call this time the "commit time". If the
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time that the transaction has been running is less than the commit
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time, ext4 will try sleeping for the commit time to see if other
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operations will join the transaction. The commit time is capped by
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the max_batch_time, which defaults to 15000us (15ms). This
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optimization can be turned off entirely by setting max_batch_time to 0.
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init_itable=n The lazy itable init code will wait n times the
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number of milliseconds it took to zero out the
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previous block group's inode table. This
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minimizes the impact on the system performance
|
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while file system's inode table is being initialized.
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min_batch_time=usec
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This parameter sets the commit time (as described above) to be at least
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min_batch_time. It defaults to zero microseconds. Increasing this
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parameter may improve the throughput of multi-threaded, synchronous
|
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workloads on very fast disks, at the cost of increasing latency.
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discard Controls whether ext4 should issue discard/TRIM
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nodiscard(*) commands to the underlying block device when
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blocks are freed. This is useful for SSD devices
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and sparse/thinly-provisioned LUNs, but it is off
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by default until sufficient testing has been done.
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journal_ioprio=prio
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The I/O priority (from 0 to 7, where 0 is the highest priority) which
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should be used for I/O operations submitted by kjournald2 during a
|
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commit operation. This defaults to 3, which is a slightly higher
|
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priority than the default I/O priority.
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nouid32 Disables 32-bit UIDs and GIDs. This is for
|
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interoperability with older kernels which only
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store and expect 16-bit values.
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auto_da_alloc(*), noauto_da_alloc
|
||||
Many broken applications don't use fsync() when replacing existing
|
||||
files via patterns such as fd = open("foo.new")/write(fd,..)/close(fd)/
|
||||
rename("foo.new", "foo"), or worse yet, fd = open("foo",
|
||||
O_TRUNC)/write(fd,..)/close(fd). If auto_da_alloc is enabled, ext4
|
||||
will detect the replace-via-rename and replace-via-truncate patterns
|
||||
and force that any delayed allocation blocks are allocated such that at
|
||||
the next journal commit, in the default data=ordered mode, the data
|
||||
blocks of the new file are forced to disk before the rename() operation
|
||||
is committed. This provides roughly the same level of guarantees as
|
||||
ext3, and avoids the "zero-length" problem that can happen when a
|
||||
system crashes before the delayed allocation blocks are forced to disk.
|
||||
|
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block_validity(*) These options enable or disable the in-kernel
|
||||
noblock_validity facility for tracking filesystem metadata blocks
|
||||
within internal data structures. This allows multi-
|
||||
block allocator and other routines to notice
|
||||
bugs or corrupted allocation bitmaps which cause
|
||||
blocks to be allocated which overlap with
|
||||
filesystem metadata blocks.
|
||||
noinit_itable
|
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Do not initialize any uninitialized inode table blocks in the
|
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background. This feature may be used by installation CD's so that the
|
||||
install process can complete as quickly as possible; the inode table
|
||||
initialization process would then be deferred until the next time the
|
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file system is unmounted.
|
||||
|
||||
dioread_lock Controls whether or not ext4 should use the DIO read
|
||||
dioread_nolock locking. If the dioread_nolock option is specified
|
||||
ext4 will allocate uninitialized extent before buffer
|
||||
write and convert the extent to initialized after IO
|
||||
completes. This approach allows ext4 code to avoid
|
||||
using inode mutex, which improves scalability on high
|
||||
speed storages. However this does not work with
|
||||
data journaling and dioread_nolock option will be
|
||||
ignored with kernel warning. Note that dioread_nolock
|
||||
code path is only used for extent-based files.
|
||||
Because of the restrictions this options comprises
|
||||
it is off by default (e.g. dioread_lock).
|
||||
init_itable=n
|
||||
The lazy itable init code will wait n times the number of milliseconds
|
||||
it took to zero out the previous block group's inode table. This
|
||||
minimizes the impact on the system performance while file system's
|
||||
inode table is being initialized.
|
||||
|
||||
max_dir_size_kb=n This limits the size of directories so that any
|
||||
attempt to expand them beyond the specified
|
||||
limit in kilobytes will cause an ENOSPC error.
|
||||
This is useful in memory constrained
|
||||
environments, where a very large directory can
|
||||
cause severe performance problems or even
|
||||
provoke the Out Of Memory killer. (For example,
|
||||
if there is only 512mb memory available, a 176mb
|
||||
directory may seriously cramp the system's style.)
|
||||
discard, nodiscard(*)
|
||||
Controls whether ext4 should issue discard/TRIM commands to the
|
||||
underlying block device when blocks are freed. This is useful for SSD
|
||||
devices and sparse/thinly-provisioned LUNs, but it is off by default
|
||||
until sufficient testing has been done.
|
||||
|
||||
i_version Enable 64-bit inode version support. This option is
|
||||
off by default.
|
||||
nouid32
|
||||
Disables 32-bit UIDs and GIDs. This is for interoperability with
|
||||
older kernels which only store and expect 16-bit values.
|
||||
|
||||
dax Use direct access (no page cache). See
|
||||
Documentation/filesystems/dax.txt. Note that
|
||||
this option is incompatible with data=journal.
|
||||
======================= =======================================================
|
||||
block_validity(*), noblock_validity
|
||||
These options enable or disable the in-kernel facility for tracking
|
||||
filesystem metadata blocks within internal data structures. This
|
||||
allows multi- block allocator and other routines to notice bugs or
|
||||
corrupted allocation bitmaps which cause blocks to be allocated which
|
||||
overlap with filesystem metadata blocks.
|
||||
|
||||
dioread_lock, dioread_nolock
|
||||
Controls whether or not ext4 should use the DIO read locking. If the
|
||||
dioread_nolock option is specified ext4 will allocate uninitialized
|
||||
extent before buffer write and convert the extent to initialized after
|
||||
IO completes. This approach allows ext4 code to avoid using inode
|
||||
mutex, which improves scalability on high speed storages. However this
|
||||
does not work with data journaling and dioread_nolock option will be
|
||||
ignored with kernel warning. Note that dioread_nolock code path is only
|
||||
used for extent-based files. Because of the restrictions this options
|
||||
comprises it is off by default (e.g. dioread_lock).
|
||||
|
||||
max_dir_size_kb=n
|
||||
This limits the size of directories so that any attempt to expand them
|
||||
beyond the specified limit in kilobytes will cause an ENOSPC error.
|
||||
This is useful in memory constrained environments, where a very large
|
||||
directory can cause severe performance problems or even provoke the Out
|
||||
Of Memory killer. (For example, if there is only 512mb memory
|
||||
available, a 176mb directory may seriously cramp the system's style.)
|
||||
|
||||
i_version
|
||||
Enable 64-bit inode version support. This option is off by default.
|
||||
|
||||
dax
|
||||
Use direct access (no page cache). See
|
||||
Documentation/filesystems/dax.txt. Note that this option is
|
||||
incompatible with data=journal.
|
||||
|
||||
Data Mode
|
||||
=========
|
||||
@ -407,11 +394,8 @@ in table below.
|
||||
|
||||
Files in /proc/fs/ext4/<devname>
|
||||
|
||||
================ =======
|
||||
File Content
|
||||
================ =======
|
||||
mb_groups details of multiblock allocator buddy cache of free blocks
|
||||
================ =======
|
||||
mb_groups
|
||||
details of multiblock allocator buddy cache of free blocks
|
||||
|
||||
/sys entries
|
||||
============
|
||||
@ -426,74 +410,71 @@ Files in /sys/fs/ext4/<devname>:
|
||||
|
||||
(see also Documentation/ABI/testing/sysfs-fs-ext4)
|
||||
|
||||
============================= =================================================
|
||||
File Content
|
||||
============================= =================================================
|
||||
delayed_allocation_blocks This file is read-only and shows the number of
|
||||
blocks that are dirty in the page cache, but
|
||||
which do not have their location in the
|
||||
filesystem allocated yet.
|
||||
delayed_allocation_blocks
|
||||
This file is read-only and shows the number of blocks that are dirty in
|
||||
the page cache, but which do not have their location in the filesystem
|
||||
allocated yet.
|
||||
|
||||
inode_goal Tuning parameter which (if non-zero) controls
|
||||
the goal inode used by the inode allocator in
|
||||
preference to all other allocation heuristics.
|
||||
This is intended for debugging use only, and
|
||||
should be 0 on production systems.
|
||||
inode_goal
|
||||
Tuning parameter which (if non-zero) controls the goal inode used by
|
||||
the inode allocator in preference to all other allocation heuristics.
|
||||
This is intended for debugging use only, and should be 0 on production
|
||||
systems.
|
||||
|
||||
inode_readahead_blks Tuning parameter which controls the maximum
|
||||
number of inode table blocks that ext4's inode
|
||||
table readahead algorithm will pre-read into
|
||||
the buffer cache
|
||||
inode_readahead_blks
|
||||
Tuning parameter which controls the maximum number of inode table
|
||||
blocks that ext4's inode table readahead algorithm will pre-read into
|
||||
the buffer cache.
|
||||
|
||||
lifetime_write_kbytes This file is read-only and shows the number of
|
||||
kilobytes of data that have been written to this
|
||||
filesystem since it was created.
|
||||
lifetime_write_kbytes
|
||||
This file is read-only and shows the number of kilobytes of data that
|
||||
have been written to this filesystem since it was created.
|
||||
|
||||
max_writeback_mb_bump The maximum number of megabytes the writeback
|
||||
code will try to write out before move on to
|
||||
another inode.
|
||||
max_writeback_mb_bump
|
||||
The maximum number of megabytes the writeback code will try to write
|
||||
out before move on to another inode.
|
||||
|
||||
mb_group_prealloc The multiblock allocator will round up allocation
|
||||
requests to a multiple of this tuning parameter if
|
||||
the stripe size is not set in the ext4 superblock
|
||||
mb_group_prealloc
|
||||
The multiblock allocator will round up allocation requests to a
|
||||
multiple of this tuning parameter if the stripe size is not set in the
|
||||
ext4 superblock
|
||||
|
||||
mb_max_to_scan The maximum number of extents the multiblock
|
||||
allocator will search to find the best extent
|
||||
mb_max_to_scan
|
||||
The maximum number of extents the multiblock allocator will search to
|
||||
find the best extent.
|
||||
|
||||
mb_min_to_scan The minimum number of extents the multiblock
|
||||
allocator will search to find the best extent
|
||||
mb_min_to_scan
|
||||
The minimum number of extents the multiblock allocator will search to
|
||||
find the best extent.
|
||||
|
||||
mb_order2_req Tuning parameter which controls the minimum size
|
||||
for requests (as a power of 2) where the buddy
|
||||
cache is used
|
||||
mb_order2_req
|
||||
Tuning parameter which controls the minimum size for requests (as a
|
||||
power of 2) where the buddy cache is used.
|
||||
|
||||
mb_stats Controls whether the multiblock allocator should
|
||||
collect statistics, which are shown during the
|
||||
unmount. 1 means to collect statistics, 0 means
|
||||
not to collect statistics
|
||||
mb_stats
|
||||
Controls whether the multiblock allocator should collect statistics,
|
||||
which are shown during the unmount. 1 means to collect statistics, 0
|
||||
means not to collect statistics.
|
||||
|
||||
mb_stream_req Files which have fewer blocks than this tunable
|
||||
parameter will have their blocks allocated out
|
||||
of a block group specific preallocation pool, so
|
||||
that small files are packed closely together.
|
||||
Each large file will have its blocks allocated
|
||||
out of its own unique preallocation pool.
|
||||
mb_stream_req
|
||||
Files which have fewer blocks than this tunable parameter will have
|
||||
their blocks allocated out of a block group specific preallocation
|
||||
pool, so that small files are packed closely together. Each large file
|
||||
will have its blocks allocated out of its own unique preallocation
|
||||
pool.
|
||||
|
||||
session_write_kbytes This file is read-only and shows the number of
|
||||
kilobytes of data that have been written to this
|
||||
filesystem since it was mounted.
|
||||
session_write_kbytes
|
||||
This file is read-only and shows the number of kilobytes of data that
|
||||
have been written to this filesystem since it was mounted.
|
||||
|
||||
reserved_clusters This is RW file and contains number of reserved
|
||||
clusters in the file system which will be used
|
||||
in the specific situations to avoid costly
|
||||
zeroout, unexpected ENOSPC, or possible data
|
||||
loss. The default is 2% or 4096 clusters,
|
||||
whichever is smaller and this can be changed
|
||||
however it can never exceed number of clusters
|
||||
in the file system. If there is not enough space
|
||||
for the reserved space when mounting the file
|
||||
mount will _not_ fail.
|
||||
============================= =================================================
|
||||
reserved_clusters
|
||||
This is RW file and contains number of reserved clusters in the file
|
||||
system which will be used in the specific situations to avoid costly
|
||||
zeroout, unexpected ENOSPC, or possible data loss. The default is 2% or
|
||||
4096 clusters, whichever is smaller and this can be changed however it
|
||||
can never exceed number of clusters in the file system. If there is not
|
||||
enough space for the reserved space when mounting the file mount will
|
||||
_not_ fail.
|
||||
|
||||
Ioctls
|
||||
======
|
||||
@ -504,100 +485,80 @@ shown in the table below.
|
||||
|
||||
Table of Ext4 specific ioctls
|
||||
|
||||
============================= =================================================
|
||||
Ioctl Description
|
||||
============================= =================================================
|
||||
EXT4_IOC_GETFLAGS Get additional attributes associated with inode.
|
||||
The ioctl argument is an integer bitfield, with
|
||||
bit values described in ext4.h. This ioctl is an
|
||||
alias for FS_IOC_GETFLAGS.
|
||||
EXT4_IOC_GETFLAGS
|
||||
Get additional attributes associated with inode. The ioctl argument is
|
||||
an integer bitfield, with bit values described in ext4.h. This ioctl is
|
||||
an alias for FS_IOC_GETFLAGS.
|
||||
|
||||
EXT4_IOC_SETFLAGS Set additional attributes associated with inode.
|
||||
The ioctl argument is an integer bitfield, with
|
||||
bit values described in ext4.h. This ioctl is an
|
||||
alias for FS_IOC_SETFLAGS.
|
||||
EXT4_IOC_SETFLAGS
|
||||
Set additional attributes associated with inode. The ioctl argument is
|
||||
an integer bitfield, with bit values described in ext4.h. This ioctl is
|
||||
an alias for FS_IOC_SETFLAGS.
|
||||
|
||||
EXT4_IOC_GETVERSION
|
||||
EXT4_IOC_GETVERSION_OLD
|
||||
Get the inode i_generation number stored for
|
||||
each inode. The i_generation number is normally
|
||||
changed only when new inode is created and it is
|
||||
particularly useful for network filesystems. The
|
||||
'_OLD' version of this ioctl is an alias for
|
||||
FS_IOC_GETVERSION.
|
||||
EXT4_IOC_GETVERSION, EXT4_IOC_GETVERSION_OLD
|
||||
Get the inode i_generation number stored for each inode. The
|
||||
i_generation number is normally changed only when new inode is created
|
||||
and it is particularly useful for network filesystems. The '_OLD'
|
||||
version of this ioctl is an alias for FS_IOC_GETVERSION.
|
||||
|
||||
EXT4_IOC_SETVERSION
|
||||
EXT4_IOC_SETVERSION_OLD
|
||||
Set the inode i_generation number stored for
|
||||
each inode. The '_OLD' version of this ioctl
|
||||
is an alias for FS_IOC_SETVERSION.
|
||||
EXT4_IOC_SETVERSION, EXT4_IOC_SETVERSION_OLD
|
||||
Set the inode i_generation number stored for each inode. The '_OLD'
|
||||
version of this ioctl is an alias for FS_IOC_SETVERSION.
|
||||
|
||||
EXT4_IOC_GROUP_EXTEND This ioctl has the same purpose as the resize
|
||||
mount option. It allows to resize filesystem
|
||||
to the end of the last existing block group,
|
||||
further resize has to be done with resize2fs,
|
||||
either online, or offline. The argument points
|
||||
to the unsigned logn number representing the
|
||||
filesystem new block count.
|
||||
EXT4_IOC_GROUP_EXTEND
|
||||
This ioctl has the same purpose as the resize mount option. It allows
|
||||
to resize filesystem to the end of the last existing block group,
|
||||
further resize has to be done with resize2fs, either online, or
|
||||
offline. The argument points to the unsigned logn number representing
|
||||
the filesystem new block count.
|
||||
|
||||
EXT4_IOC_MOVE_EXT Move the block extents from orig_fd (the one
|
||||
this ioctl is pointing to) to the donor_fd (the
|
||||
one specified in move_extent structure passed
|
||||
as an argument to this ioctl). Then, exchange
|
||||
inode metadata between orig_fd and donor_fd.
|
||||
This is especially useful for online
|
||||
defragmentation, because the allocator has the
|
||||
opportunity to allocate moved blocks better,
|
||||
ideally into one contiguous extent.
|
||||
EXT4_IOC_MOVE_EXT
|
||||
Move the block extents from orig_fd (the one this ioctl is pointing to)
|
||||
to the donor_fd (the one specified in move_extent structure passed as
|
||||
an argument to this ioctl). Then, exchange inode metadata between
|
||||
orig_fd and donor_fd. This is especially useful for online
|
||||
defragmentation, because the allocator has the opportunity to allocate
|
||||
moved blocks better, ideally into one contiguous extent.
|
||||
|
||||
EXT4_IOC_GROUP_ADD Add a new group descriptor to an existing or
|
||||
new group descriptor block. The new group
|
||||
descriptor is described by ext4_new_group_input
|
||||
structure, which is passed as an argument to
|
||||
this ioctl. This is especially useful in
|
||||
conjunction with EXT4_IOC_GROUP_EXTEND,
|
||||
which allows online resize of the filesystem
|
||||
to the end of the last existing block group.
|
||||
Those two ioctls combined is used in userspace
|
||||
online resize tool (e.g. resize2fs).
|
||||
EXT4_IOC_GROUP_ADD
|
||||
Add a new group descriptor to an existing or new group descriptor
|
||||
block. The new group descriptor is described by ext4_new_group_input
|
||||
structure, which is passed as an argument to this ioctl. This is
|
||||
especially useful in conjunction with EXT4_IOC_GROUP_EXTEND, which
|
||||
allows online resize of the filesystem to the end of the last existing
|
||||
block group. Those two ioctls combined is used in userspace online
|
||||
resize tool (e.g. resize2fs).
|
||||
|
||||
EXT4_IOC_MIGRATE This ioctl operates on the filesystem itself.
|
||||
It converts (migrates) ext3 indirect block mapped
|
||||
inode to ext4 extent mapped inode by walking
|
||||
through indirect block mapping of the original
|
||||
inode and converting contiguous block ranges
|
||||
into ext4 extents of the temporary inode. Then,
|
||||
inodes are swapped. This ioctl might help, when
|
||||
migrating from ext3 to ext4 filesystem, however
|
||||
suggestion is to create fresh ext4 filesystem
|
||||
and copy data from the backup. Note, that
|
||||
filesystem has to support extents for this ioctl
|
||||
to work.
|
||||
EXT4_IOC_MIGRATE
|
||||
This ioctl operates on the filesystem itself. It converts (migrates)
|
||||
ext3 indirect block mapped inode to ext4 extent mapped inode by walking
|
||||
through indirect block mapping of the original inode and converting
|
||||
contiguous block ranges into ext4 extents of the temporary inode. Then,
|
||||
inodes are swapped. This ioctl might help, when migrating from ext3 to
|
||||
ext4 filesystem, however suggestion is to create fresh ext4 filesystem
|
||||
and copy data from the backup. Note, that filesystem has to support
|
||||
extents for this ioctl to work.
|
||||
|
||||
EXT4_IOC_ALLOC_DA_BLKS Force all of the delay allocated blocks to be
|
||||
allocated to preserve application-expected ext3
|
||||
behaviour. Note that this will also start
|
||||
triggering a write of the data blocks, but this
|
||||
behaviour may change in the future as it is
|
||||
not necessary and has been done this way only
|
||||
for sake of simplicity.
|
||||
EXT4_IOC_ALLOC_DA_BLKS
|
||||
Force all of the delay allocated blocks to be allocated to preserve
|
||||
application-expected ext3 behaviour. Note that this will also start
|
||||
triggering a write of the data blocks, but this behaviour may change in
|
||||
the future as it is not necessary and has been done this way only for
|
||||
sake of simplicity.
|
||||
|
||||
EXT4_IOC_RESIZE_FS Resize the filesystem to a new size. The number
|
||||
of blocks of resized filesystem is passed in via
|
||||
64 bit integer argument. The kernel allocates
|
||||
bitmaps and inode table, the userspace tool thus
|
||||
just passes the new number of blocks.
|
||||
EXT4_IOC_RESIZE_FS
|
||||
Resize the filesystem to a new size. The number of blocks of resized
|
||||
filesystem is passed in via 64 bit integer argument. The kernel
|
||||
allocates bitmaps and inode table, the userspace tool thus just passes
|
||||
the new number of blocks.
|
||||
|
||||
EXT4_IOC_SWAP_BOOT Swap i_blocks and associated attributes
|
||||
(like i_blocks, i_size, i_flags, ...) from
|
||||
the specified inode with inode
|
||||
EXT4_BOOT_LOADER_INO (#5). This is typically
|
||||
used to store a boot loader in a secure part of
|
||||
the filesystem, where it can't be changed by a
|
||||
normal user by accident.
|
||||
The data blocks of the previous boot loader
|
||||
will be associated with the given inode.
|
||||
============================= =================================================
|
||||
EXT4_IOC_SWAP_BOOT
|
||||
Swap i_blocks and associated attributes (like i_blocks, i_size,
|
||||
i_flags, ...) from the specified inode with inode EXT4_BOOT_LOADER_INO
|
||||
(#5). This is typically used to store a boot loader in a secure part of
|
||||
the filesystem, where it can't be changed by a normal user by accident.
|
||||
The data blocks of the previous boot loader will be associated with the
|
||||
given inode.
|
||||
|
||||
References
|
||||
==========
|
||||
|
||||
Loading…
Reference in New Issue
Block a user