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diff --git a/Documentation/filesystems/btrfs.txt b/Documentation/filesystems/btrfs.txt deleted file mode 100644 index b349d57b76ea..000000000000 --- a/Documentation/filesystems/btrfs.txt +++ /dev/null @@ -1,257 +0,0 @@ - -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. - -The main Btrfs features include: - - * Extent based file storage (2^64 max file size) - * Space efficient packing of small files - * Space efficient indexed directories - * Dynamic inode allocation - * Writable snapshots - * Subvolumes (separate internal filesystem roots) - * Object level mirroring and striping - * 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) - * Online filesystem defragmentation - - -Mount Options -============= - -When mounting a btrfs filesystem, the following option are accepted. -Unless otherwise specified, all options default to off. - - 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. - - autodefrag - Detect 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. - - 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. Especialy useful when trying to mount a multi-device - setup as root. May be specified multiple times for multiple devices. - - discard - Issue 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). - - enospc_debug - 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. - - 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 sectorsize, 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. - - noacl - Disable support for Posix Access Control Lists (ACLs). See the - acl(5) manual page for more information about ACLs. - - nobarrier - Disables 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 used on a device with a volatile (non-battery-backed) - write-back cache, this option will lead to filesystem corruption on a - system crash or power loss. - - nodatacow - Disable data copy-on-write for newly created files. Implies nodatasum, - and disables all compression. - - nodatasum - Disable data checksumming for newly created files. - - notreelog - 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. - - 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 nonrotational 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 - -btrfsctl: control program to create snapshots and subvolumes: - - mount /dev/sda2 /mnt - btrfsctl -s new_subvol_name /mnt - btrfsctl -s snapshot_of_default /mnt/default - btrfsctl -s snapshot_of_new_subvol /mnt/new_subvol_name - btrfsctl -s snapshot_of_a_snapshot /mnt/snapshot_of_new_subvol - ls /mnt - default snapshot_of_a_snapshot snapshot_of_new_subvol - new_subvol_name snapshot_of_default - - Snapshots and subvolumes cannot be deleted right now, but you can - rm -rf all the files and directories inside them. - -btrfsck: do a limited check of the FS extent trees. - -btrfs-debug-tree: print all of the FS metadata in text form. Example: - - btrfs-debug-tree /dev/sda2 >& big_output_file |