-
BTRFS
=====
-Btrfs is a copy on write filesystem for Linux aimed at
-implementing advanced features while focusing on fault tolerance,
-repair and easy administration. Initially developed by Oracle, Btrfs
-is licensed under the GPL and open for contribution from anyone.
-
-Linux has a wealth of filesystems to choose from, but we are facing a
-number of challenges with scaling to the large storage subsystems that
-are becoming common in today's data centers. Filesystems need to scale
-in their ability to address and manage large storage, and also in
-their ability to detect, repair and tolerate errors in the data stored
-on disk. Btrfs is under heavy development, and is not suitable for
-any uses other than benchmarking and review. The Btrfs disk format is
-not yet finalized.
+Btrfs is a copy on write filesystem for Linux aimed at implementing advanced
+features while focusing on fault tolerance, repair and easy administration.
+Jointly developed by several companies, licensed under the GPL and open for
+contribution from anyone.
The main Btrfs features include:
* Checksums on data and metadata (multiple algorithms available)
* Compression
* Integrated multiple device support, with several raid algorithms
- * Online filesystem check (not yet implemented)
- * Very fast offline filesystem check
- * Efficient incremental backup and FS mirroring (not yet implemented)
+ * Offline filesystem check
+ * Efficient incremental backup and FS mirroring
* Online filesystem defragmentation
+For more information please refer to the wiki
-Mount Options
-=============
-
-When mounting a btrfs filesystem, the following option are accepted.
-Options with (*) are default options and will not show in the mount options.
-
- alloc_start=<bytes>
- Debugging option to force all block allocations above a certain
- byte threshold on each block device. The value is specified in
- bytes, optionally with a K, M, or G suffix, case insensitive.
- Default is 1MB.
-
- noautodefrag(*)
- autodefrag
- Disable/enable auto defragmentation.
- Auto defragmentation detects small random writes into files and queue
- them up for the defrag process. Works best for small files;
- Not well suited for large database workloads.
-
- check_int
- check_int_data
- check_int_print_mask=<value>
- These debugging options control the behavior of the integrity checking
- module (the BTRFS_FS_CHECK_INTEGRITY config option required).
-
- check_int enables the integrity checker module, which examines all
- block write requests to ensure on-disk consistency, at a large
- memory and CPU cost.
-
- check_int_data includes extent data in the integrity checks, and
- implies the check_int option.
-
- check_int_print_mask takes a bitmask of BTRFSIC_PRINT_MASK_* values
- as defined in fs/btrfs/check-integrity.c, to control the integrity
- checker module behavior.
-
- See comments at the top of fs/btrfs/check-integrity.c for more info.
-
- commit=<seconds>
- Set the interval of periodic commit, 30 seconds by default. Higher
- values defer data being synced to permanent storage with obvious
- consequences when the system crashes. The upper bound is not forced,
- but a warning is printed if it's more than 300 seconds (5 minutes).
-
- compress
- compress=<type>
- compress-force
- compress-force=<type>
- Control BTRFS file data compression. Type may be specified as "zlib"
- "lzo" or "no" (for no compression, used for remounting). If no type
- is specified, zlib is used. If compress-force is specified,
- all files will be compressed, whether or not they compress well.
- If compression is enabled, nodatacow and nodatasum are disabled.
-
- degraded
- Allow mounts to continue with missing devices. A read-write mount may
- fail with too many devices missing, for example if a stripe member
- is completely missing.
-
- device=<devicepath>
- Specify a device during mount so that ioctls on the control device
- can be avoided. Especially useful when trying to mount a multi-device
- setup as root. May be specified multiple times for multiple devices.
-
- nodiscard(*)
- discard
- Disable/enable discard mount option.
- Discard issues frequent commands to let the block device reclaim space
- freed by the filesystem.
- This is useful for SSD devices, thinly provisioned
- LUNs and virtual machine images, but may have a significant
- performance impact. (The fstrim command is also available to
- initiate batch trims from userspace).
-
- noenospc_debug(*)
- enospc_debug
- Disable/enable debugging option to be more verbose in some ENOSPC conditions.
-
- fatal_errors=<action>
- Action to take when encountering a fatal error:
- "bug" - BUG() on a fatal error. This is the default.
- "panic" - panic() on a fatal error.
-
- noflushoncommit(*)
- flushoncommit
- The 'flushoncommit' mount option forces any data dirtied by a write in a
- prior transaction to commit as part of the current commit. This makes
- the committed state a fully consistent view of the file system from the
- application's perspective (i.e., it includes all completed file system
- operations). This was previously the behavior only when a snapshot is
- created.
-
- inode_cache
- Enable free inode number caching. Defaults to off due to an overflow
- problem when the free space crcs don't fit inside a single page.
-
- max_inline=<bytes>
- Specify the maximum amount of space, in bytes, that can be inlined in
- a metadata B-tree leaf. The value is specified in bytes, optionally
- with a K, M, or G suffix, case insensitive. In practice, this value
- is limited by the root sector size, with some space unavailable due
- to leaf headers. For a 4k sector size, max inline data is ~3900 bytes.
-
- metadata_ratio=<value>
- Specify that 1 metadata chunk should be allocated after every <value>
- data chunks. Off by default.
-
- acl(*)
- noacl
- Enable/disable support for Posix Access Control Lists (ACLs). See the
- acl(5) manual page for more information about ACLs.
-
- barrier(*)
- nobarrier
- Enable/disable the use of block layer write barriers. Write barriers
- ensure that certain IOs make it through the device cache and are on
- persistent storage. If disabled on a device with a volatile
- (non-battery-backed) write-back cache, nobarrier option will lead to
- filesystem corruption on a system crash or power loss.
-
- datacow(*)
- nodatacow
- Enable/disable data copy-on-write for newly created files.
- Nodatacow implies nodatasum, and disables all compression.
-
- datasum(*)
- nodatasum
- Enable/disable data checksumming for newly created files.
- Datasum implies datacow.
-
- treelog(*)
- notreelog
- Enable/disable the tree logging used for fsync and O_SYNC writes.
-
- nologreplay
- Disable the log tree replay at mount time to prevent filesystem
- from getting modified.
- Must be used with 'ro' mount option.
- A filesystem mounted with this option cannot transition to a
- read-write mount via remount,rw - the filesystem must be unmounted
- and mounted back again if read-write access is desired.
-
- usebackuproot
- Enable attempts to use backup tree roots if a bad tree root is found at
- mount time.
- Currently this scans a list of 4 previous tree roots and tries to
- use the first readable.
- And since the mount option doesn't affect any behavior after mount,
- it won't be shown in mount info.
- Prior to 4.6, this was done by 'recovery' option that has been
- deprecated, but will work.
-
- rescan_uuid_tree
- Force check and rebuild procedure of the UUID tree. This should not
- normally be needed.
-
- skip_balance
- Skip automatic resume of interrupted balance operation after mount.
- May be resumed with "btrfs balance resume."
-
- space_cache (*)
- Enable the on-disk freespace cache.
- nospace_cache
- Disable freespace cache loading without clearing the cache.
- clear_cache
- Force clearing and rebuilding of the disk space cache if something
- has gone wrong.
-
- ssd
- nossd
- ssd_spread
- Options to control ssd allocation schemes. By default, BTRFS will
- enable or disable ssd allocation heuristics depending on whether a
- rotational or non-rotational disk is in use. The ssd and nossd options
- can override this autodetection.
-
- The ssd_spread mount option attempts to allocate into big chunks
- of unused space, and may perform better on low-end ssds. ssd_spread
- implies ssd, enabling all other ssd heuristics as well.
-
- subvol=<path>
- Mount subvolume at <path> rather than the root subvolume. <path> is
- relative to the top level subvolume.
-
- subvolid=<ID>
- Mount subvolume specified by an ID number rather than the root subvolume.
- This allows mounting of subvolumes which are not in the root of the mounted
- filesystem.
- You can use "btrfs subvolume list" to see subvolume ID numbers.
-
- subvolrootid=<objectid> (deprecated)
- Mount subvolume specified by <objectid> rather than the root subvolume.
- This allows mounting of subvolumes which are not in the root of the mounted
- filesystem.
- You can use "btrfs subvolume show " to see the object ID for a subvolume.
-
- thread_pool=<number>
- The number of worker threads to allocate. The default number is equal
- to the number of CPUs + 2, or 8, whichever is smaller.
-
- user_subvol_rm_allowed
- Allow subvolumes to be deleted by a non-root user. Use with caution.
-
-MAILING LIST
-============
-
-There is a Btrfs mailing list hosted on vger.kernel.org. You can
-find details on how to subscribe here:
-
-http://vger.kernel.org/vger-lists.html#linux-btrfs
-
-Mailing list archives are available from gmane:
-
-http://dir.gmane.org/gmane.comp.file-systems.btrfs
-
-
-
-IRC
-===
-
-Discussion of Btrfs also occurs on the #btrfs channel of the Freenode
-IRC network.
-
-
-
- UTILITIES
- =========
-
-Userspace tools for creating and manipulating Btrfs file systems are
-available from the git repository at the following location:
-
- http://git.kernel.org/?p=linux/kernel/git/mason/btrfs-progs.git
- git://git.kernel.org/pub/scm/linux/kernel/git/mason/btrfs-progs.git
-
-These include the following tools:
-
-* mkfs.btrfs: create a filesystem
-
-* btrfs: a single tool to manage the filesystems, refer to the manpage for more details
-
-* 'btrfsck' or 'btrfs check': do a consistency check of the filesystem
-
-Other tools for specific tasks:
-
-* btrfs-convert: in-place conversion from ext2/3/4 filesystems
+ https://btrfs.wiki.kernel.org
-* btrfs-image: dump filesystem metadata for debugging
+that maintains information about administration tasks, frequently asked
+questions, use cases, mount options, comprehensible changelogs, features,
+manual pages, source code repositories, contacts etc.
git.samba.org / sfrench / cifs-2.6.git / blobdiff