[[storage_btrfs]]
BTRFS Backend
-------------
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:pve-toplevel:
:title: Storage: BTRFS
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Storage pool type: `btrfs`

On the surface, this storage type is very similar to the directory storage type,
so see the directory backend section for a general overview.

The main difference is that with this storage type `raw` formatted disks will be
placed in a subvolume, in order to allow taking snapshots and supporting offline
storage migration with snapshots being preserved.

NOTE: BTRFS will honor the `O_DIRECT` flag when opening files, meaning VMs
should not use cache mode `none`, otherwise there will be checksum errors.

Configuration
~~~~~~~~~~~~~

This backend is configured similarly to the directory storage. Note that when
adding a directory as a BTRFS storage, which is not itself also the mount point,
it is highly recommended to specify the actual mount point via the
`is_mountpoint` option.

For example, if a BTRFS file system is mounted at `/mnt/data2` and its
`pve-storage/` subdirectory (which may be a snapshot, which is recommended)
should be added as a storage pool called `data2`, you can use the following
entry:

----
btrfs: data2
        path /mnt/data2/pve-storage
        content rootdir,images
        is_mountpoint /mnt/data2
----

Snapshots
~~~~~~~~~

When taking a snapshot of a subvolume or `raw` file, the snapshot will be
created as a read-only subvolume with the same path followed by an `@` and the
snapshot's name.

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See Also
~~~~~~~~

* link:/wiki/Storage[Storage]
* link:/wiki/BTRFS[BTRFS Sysadmin]

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