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.