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@@ -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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-
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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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-
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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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-
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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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-
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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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-
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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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-
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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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-
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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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-
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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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-
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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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-
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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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-
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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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-
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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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-
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-bsddf (*) Make 'df' act like BSD.
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-minixdf Make 'df' act like Minix.
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-
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-debug Extra debugging information is sent to syslog.
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-
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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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-
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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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-
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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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-
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-grpid New objects have the group ID of their parent.
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-bsdgroups
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-
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-nogrpid (*) New objects have the group ID of their creator.
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-sysvgroups
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-
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-resgid=n The group ID which may use the reserved blocks.
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-
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-resuid=n The user ID which may use the reserved blocks.
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-
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-sb=n Use alternate superblock at this location.
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-
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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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-
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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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-
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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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-
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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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-
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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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-
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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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-
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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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-
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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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-
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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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-
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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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-
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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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-
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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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-
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-block_validity(*) These options enable or disable the in-kernel
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-noblock_validity facility for tracking filesystem metadata blocks
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- within internal data structures. This allows multi-
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- block allocator and other routines to notice
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- bugs or corrupted allocation bitmaps which cause
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- blocks to be allocated which overlap with
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- filesystem metadata blocks.
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-
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-dioread_lock Controls whether or not ext4 should use the DIO read
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-dioread_nolock locking. If the dioread_nolock option is specified
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- ext4 will allocate uninitialized extent before buffer
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- write and convert the extent to initialized after IO
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- completes. This approach allows ext4 code to avoid
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- using inode mutex, which improves scalability on high
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- speed storages. However this does not work with
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- data journaling and dioread_nolock option will be
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- ignored with kernel warning. Note that dioread_nolock
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- code path is only used for extent-based files.
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- Because of the restrictions this options comprises
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- it is off by default (e.g. dioread_lock).
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-
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-max_dir_size_kb=n This limits the size of directories so that any
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- attempt to expand them beyond the specified
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- limit in kilobytes will cause an ENOSPC error.
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- This is useful in memory constrained
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- environments, where a very large directory can
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- cause severe performance problems or even
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- provoke the Out Of Memory killer. (For example,
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- if there is only 512mb memory available, a 176mb
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- directory may seriously cramp the system's style.)
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-
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-i_version Enable 64-bit inode version support. This option is
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- off by default.
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-
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-dax Use direct access (no page cache). See
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- Documentation/filesystems/dax.txt. Note that
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- this option is incompatible with data=journal.
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-======================= =======================================================
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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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+
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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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+
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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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+
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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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+
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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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+
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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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+
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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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+
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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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+
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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
|
|
|
+ default value (or any low value) will hurt performance, but it's good
|
|
|
+ for data-safety. Setting it to 0 will have the same effect as leaving
|
|
|
+ it at the default (5 seconds). Setting it to very large values will
|
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+ improve performance.
|
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+
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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
|
|
|
+ caches safe to use, at some performance penalty. If your disks are
|
|
|
+ battery-backed in one way or another, disabling barriers may safely
|
|
|
+ improve performance. The mount options "barrier" and "nobarrier" can
|
|
|
+ also be used to enable or disable barriers, for consistency with other
|
|
|
+ ext4 mount options.
|
|
|
+
|
|
|
+ inode_readahead_blks=n
|
|
|
+ This tuning parameter controls the maximum number of inode table blocks
|
|
|
+ that ext4's inode table readahead algorithm will pre-read into the
|
|
|
+ buffer cache. The default value is 32 blocks.
|
|
|
+
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+ nouser_xattr
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|
+ Disables Extended User Attributes. See the attr(5) manual page for
|
|
|
+ more information about extended attributes.
|
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|
+
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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
|
|
|
+ information about acl.
|
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+
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+ bsddf (*)
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+ Make 'df' act like BSD.
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+
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+ minixdf
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+ Make 'df' act like Minix.
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+
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+ debug
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+ Extra debugging information is sent to syslog.
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+
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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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+
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+ errors=remount-ro
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+ Remount the filesystem read-only on an error.
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+
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+ errors=continue
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+ Keep going on a filesystem error.
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+
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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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+
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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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+
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+ grpid | bsdgroups
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+ New objects have the group ID of their parent.
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+
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+ nogrpid (*) | sysvgroups
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+ New objects have the group ID of their creator.
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+
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+ resgid=n
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+ The group ID which may use the reserved blocks.
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+
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+ resuid=n
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+ The user ID which may use the reserved blocks.
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+
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+ sb=
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+ Use alternate superblock at this location.
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+
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+ quota, noquota, grpquota, usrquota
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|
+ These options are ignored by the filesystem. They are used only by
|
|
|
+ quota tools to recognize volumes where quota should be turned on. See
|
|
|
+ documentation in the quota-tools package for more details
|
|
|
+ (http://sourceforge.net/projects/linuxquota).
|
|
|
+
|
|
|
+ jqfmt=<quota type>, usrjquota=<file>, grpjquota=<file>
|
|
|
+ These options tell filesystem details about quota so that quota
|
|
|
+ information can be properly updated during journal replay. They replace
|
|
|
+ the above quota options. See documentation in the quota-tools package
|
|
|
+ for more details (http://sourceforge.net/projects/linuxquota).
|
|
|
+
|
|
|
+ stripe=n
|
|
|
+ Number of filesystem blocks that mballoc will try to use for allocation
|
|
|
+ size and alignment. For RAID5/6 systems this should be the number of
|
|
|
+ data disks * RAID chunk size in file system blocks.
|
|
|
+
|
|
|
+ delalloc (*)
|
|
|
+ Defer block allocation until just before ext4 writes out the block(s)
|
|
|
+ in question. This allows ext4 to better allocation decisions more
|
|
|
+ efficiently.
|
|
|
+
|
|
|
+ nodelalloc
|
|
|
+ Disable delayed allocation. Blocks are allocated when the data is
|
|
|
+ copied from userspace to the page cache, either via the write(2) system
|
|
|
+ call or when an mmap'ed page which was previously unallocated is
|
|
|
+ written for the first time.
|
|
|
+
|
|
|
+ max_batch_time=usec
|
|
|
+ Maximum amount of time ext4 should wait for additional filesystem
|
|
|
+ operations to be batch together with a synchronous write operation.
|
|
|
+ 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
|
|
|
+ measuring the amount of time (on average) that it takes to finish
|
|
|
+ committing a transaction. Call this time the "commit time". If the
|
|
|
+ time that the transaction has been running is less than the commit
|
|
|
+ time, ext4 will try sleeping for the commit time to see if other
|
|
|
+ operations will join the transaction. The commit time is capped by
|
|
|
+ the max_batch_time, which defaults to 15000us (15ms). This
|
|
|
+ optimization can be turned off entirely by setting max_batch_time to 0.
|
|
|
+
|
|
|
+ min_batch_time=usec
|
|
|
+ This parameter sets the commit time (as described above) to be at least
|
|
|
+ min_batch_time. It defaults to zero microseconds. Increasing this
|
|
|
+ parameter may improve the throughput of multi-threaded, synchronous
|
|
|
+ workloads on very fast disks, at the cost of increasing latency.
|
|
|
+
|
|
|
+ journal_ioprio=prio
|
|
|
+ The I/O priority (from 0 to 7, where 0 is the highest priority) which
|
|
|
+ should be used for I/O operations submitted by kjournald2 during a
|
|
|
+ commit operation. This defaults to 3, which is a slightly higher
|
|
|
+ priority than the default I/O priority.
|
|
|
+
|
|
|
+ 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.
|
|
|
+
|
|
|
+ noinit_itable
|
|
|
+ Do not initialize any uninitialized inode table blocks in the
|
|
|
+ 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
|
|
|
+ file system is unmounted.
|
|
|
+
|
|
|
+ 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.
|
|
|
+
|
|
|
+ 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.
|
|
|
+
|
|
|
+ nouid32
|
|
|
+ Disables 32-bit UIDs and GIDs. This is for interoperability with
|
|
|
+ older kernels which only store and expect 16-bit values.
|
|
|
+
|
|
|
+ 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.
|
|
|
-
|
|
|
-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
|
|
|
-
|
|
|
-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.
|
|
|
-
|
|
|
- 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_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_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.
|
|
|
-
|
|
|
- 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.
|
|
|
-============================= =================================================
|
|
|
+ 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_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.
|
|
|
+
|
|
|
+ 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_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_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_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.
|
|
|
+
|
|
|
+ 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_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_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_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_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_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_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_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_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_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_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_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
|
|
|
==========
|
Darrick J. Wong