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diff --git a/Documentation/btrfs-mount.txt b/Documentation/btrfs-mount.txt new file mode 100644 index 00000000..4433a784 --- /dev/null +++ b/Documentation/btrfs-mount.txt @@ -0,0 +1,186 @@ +btrfs-mount(5) +============== + +NAME +---- +btrfs-mount - mount options for the btrfs filesystem + +DESCRIPTION +----------- +This document describes mount options specific to the btrfs filesystem. +Other generic mount options are available,and are described in the +`mount`(8) manpage. + +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. + +*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. + +*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). + +*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. + +*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*:: + Enable/disable support for Posix Access Control Lists (ACLs). See the + `acl`(5) manual page for more information about ACLs. + +*nobarrier*:: + 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. + +*nodatacow*:: + Enable/disable data copy-on-write for newly created files. + Nodatacow implies nodatasum, and disables all compression. + +*nodatasum*:: + Enable/disable data checksumming for newly created files. + Datasum implies datacow. + +*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." + +*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. The + '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. + +SEE ALSO +-------- +`mkfs.btrfs`(8), +`mount`(8), +`btrfs`(8) |