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Diffstat (limited to 'Documentation/filesystems/btrfs.txt')
| -rw-r--r-- | Documentation/filesystems/btrfs.txt | 261 |
1 files changed, 11 insertions, 250 deletions
diff --git a/Documentation/filesystems/btrfs.txt b/Documentation/filesystems/btrfs.txt index c772b47e7..f9dad22d9 100644 --- a/Documentation/filesystems/btrfs.txt +++ b/Documentation/filesystems/btrfs.txt @@ -1,20 +1,10 @@ - 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: @@ -28,243 +18,14 @@ 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. - - recovery - Enable autorecovery attempts if a bad tree root is found at mount time. - Currently this scans a list of several previous tree roots and tries to - use the first readable. - - 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. |