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Diffstat (limited to 'Documentation/btrfs-subvolume.asciidoc')
| -rw-r--r-- | Documentation/btrfs-subvolume.asciidoc | 47 |
1 files changed, 26 insertions, 21 deletions
diff --git a/Documentation/btrfs-subvolume.asciidoc b/Documentation/btrfs-subvolume.asciidoc index fb64aa4a..2044b07d 100644 --- a/Documentation/btrfs-subvolume.asciidoc +++ b/Documentation/btrfs-subvolume.asciidoc @@ -3,7 +3,7 @@ btrfs-subvolume(8) NAME ---- -btrfs-subvolume - control btrfs subvolume(s) +btrfs-subvolume - manage btrfs subvolumes SYNOPSIS -------- @@ -11,35 +11,39 @@ SYNOPSIS DESCRIPTION ----------- -*btrfs subvolume* is used to control the filesystem to create/delete/list/show -subvolumes and snapshots. +*btrfs subvolume* is used to create/delete/list/show btrfs subvolumes and +snapshots. SUBVOLUME AND SNAPSHOT ---------------------- -A subvolume in btrfs is not like an LVM logical volume, which is quite -independent from each other, a btrfs subvolume has its hierarchy and relations -between other subvolumes. -A subvolume in btrfs can be accessed in two ways. +A subvolume is a part of filesystem with it's own and independent +file/directory hierarchy. Subvolumes can share file extents. A snapshot is +also subvolume, but with a given initial content of the original subvolume. -1. From the parent subvolume + -When accessing from the parent subvolume, the subvolume can be used just -like a directory. It can have child subvolumes and its own files/directories. +NOTE: A subvolume in btrfs is not like an LVM logical volume, which is +block-level snapshot while btrfs subvolumes are file extent-based. -2. Separate mounted filesystem + -When `mount`(8) using 'subvol' or 'subvolid' mount option, one can access -files/directories/subvolumes inside it, but nothing in parent subvolumes. +A subvolume looks like a normal directory, with some additional operations +described below. Subvolumes can be renamed or moved, nesting subvolumes is not +restricted but has some implications regarding snapshotting. -Also every btrfs filesystem has a default subvolume as its initially top-level -subvolume, whose subvolume id is 5. (0 is also acceptable as an alias.) +A subvolume in btrfs can be accessed in two ways: -A btrfs snapshot is much like a subvolume, but shares its data(and metadata) -with other subvolume/snapshot. Due to the capabilities of COW, modifications -inside a snapshot will only show in a snapshot but not in its source subvolume. +* like any other directory that is accessible to the user +* like a separately mounted filesystem (options 'subvol' or 'subvolid') -Although in btrfs, subvolumes/snapshots are treated as directories, only -subvolume/snapshot can be the source of a snapshot, snapshot can not be made -from normal directories. +In the latter case the parent directory is not visible and accessible. This is +similar to a bind mount, and in fact the subvolume mount does exactly that. + +A freshly created filesystem is also a subvolume, called 'top-level', +internally has an id 5. This subvolume cannot be removed or replaced by another +subvolume. This is also the subvolume that will be mounted by default, unless +the default subvolume has been changed (see subcommand 'set-default'). + +A snapshot is a subvolume like any other, with given initial content. By +default, snapshots are created read-write. File modifications in a snapshot +do not affect the files in the original subvolume. SUBCOMMAND ----------- @@ -178,5 +182,6 @@ further details. SEE ALSO -------- `mkfs.btrfs`(8), +`mount`(8), `btrfs-quota`(8), `btrfs-qgroup`(8), |