Btrfs/Mount Options
From Forza's ramblings
Mount options[edit | edit source]
Btrfs has many mount options that controls how the filesystem behaves.
The full set of mount options are available in the Btrfs man page.
| Mount option | Description |
|---|---|
| noatime | Disables atime updates. This is good to use by default because atime updates increases metadata writes. Atimes are especially costly performance-wise when you have many snapshots. |
| compress=<algo> | Enables compression on the filesystem. |
| compress-force=<algo> | Forces compression, even on data that doesn't compress well. Can increase compression ratio. Also increases fragmentation. |
| <algo> can be any of zlib:1-9, lzo and zstd:1-15. | |
| space_cache=v2 | Enables the new B-tree version of space cache. It is much more performant on large filesystems than The original v1. See Btrfs/Space Cache for details. |
| subvol=<subvol> | Specifies what subvolume to mount. |
| subvolid=<id> | Specifies what subvolume to mount using its ID. Can be used instead of subvol
|
| degraded | Is used to mount a filesystem that has a missing disk. Works with a redundant profile such as RAID 1. |
The basic mount command is mount -o <options> <device> <path>
# mount -o noatime,compress=zstd,subvol=my-vault /dev/sdc1 /media/vault
fstab[edit | edit source]
This is fstab on one of my machines. The disk is an SSD so I use compress-force=zstd:2 to reduce amount of data written to the disk, increasing its life span.
/etc/fstab
UUID=446d32cb-a6da-45f0-9246-1483ad3420e0 / btrfs compress-force=zstd:2,noatime,subvol=volume/root 0 0 UUID=446d32cb-a6da-45f0-9246-1483ad3420e0 /home btrfs compress-force=zstd:2,noatime,subvol=volume/home 0 0 UUID=446d32cb-a6da-45f0-9246-1483ad3420e0 /var/tmp btrfs compress-force=zstd:2,noatime,noexec,subvol=volume/var_tmp 0 0 UUID=446d32cb-a6da-45f0-9246-1483ad3420e0 /mnt/rootvol/ btrfs compress-force=zstd:2,noatime 0 0 tmpfs /tmp tmpfs rw,nosuid,noexec,nodev,size=4G,mode=1777 0 0
/mnt/rootvol is where the filesystem top level subvolume mounted. From here it is possible to access all snapshots and subvolumes directly.
Many distributions prefix subvolume names with @ so it is easier to distinguish them from normal directories.
Take a moment to read up on flat vs nested subvolume layouts over at Btrfs/Getting_Started#Subvolumes
