---
title: btrfs
subtile: tips for working with btrfs
toc: true
---

See [luks and btrfs](howto_luks_and_btrfs.html) for using encrypted
devices with btrfs.

create btrfs pool and filesystem
--------------------------------

*TODO MAKE THIS BETTER, this is just scratch stuff, don't follow blindly*

```
losetup /dev/loop1 /tmp/empty
mkfs.btrfs -m raid1 -d raid1 -L btrfs-pool /dev/sdd /dev/loop1
losetup -d /dev/loop1
rm /tmp/empty
mkfs.btrfs -L arch /dev/sda
mount /dev/sda /mnt
cd /mnt
btrfs subvolume create root
btrfs subvolume create home
umount /mnt
```

btrfs filesystem show
---------------------

Show the structure of a filesystem

```
# btrfs fi sh
Label: 'btrfs-pool'  uuid: 12345678-1234-1234-1234-123456789012
    Total devices 4 FS bytes used 8.01TiB
    devid    1 size 5.46TiB used 5.46TiB path /dev/mapper/luks1
    devid    2 size 2.73TiB used 2.73TiB path /dev/mapper/luks2
    devid    3 size 2.73TiB used 2.73TiB path /dev/mapper/luks3
    devid    5 size 5.46TiB used 5.46TiB path /dev/sdd
```

btrfs filesystem usage
----------------------

Summarize disk usage of each file

```
# btrfs fi usage -h /mnt/btrfs-pool/
Overall:
    Device size:          16.37TiB
    Device allocated:         16.37TiB
    Device unallocated:        6.00GiB
    Device missing:          0.00B
    Used:             16.02TiB
    Free (estimated):        180.76GiB  (min: 180.76GiB)
    Data ratio:               2.00
    Metadata ratio:           2.00
    Global reserve:      512.00MiB  (used: 0.00B)

Data,RAID1: Size:8.17TiB, Used:8.00TiB
   /dev/mapper/luks1       5.45TiB
   /dev/mapper/luks2       2.72TiB
   /dev/mapper/luks3       2.73TiB
   /dev/sdd    5.45TiB

Metadata,RAID1: Size:10.00GiB, Used:8.93GiB
   /dev/mapper/luks1       9.00GiB
   /dev/mapper/luks2       5.00GiB
   /dev/mapper/luks3       1.00GiB
   /dev/sdd    5.00GiB

System,RAID1: Size:32.00MiB, Used:1.30MiB
   /dev/mapper/luks1      32.00MiB
   /dev/sdd   32.00MiB

Unallocated:
   /dev/mapper/luks1       2.00GiB
   /dev/mapper/luks2       1.02MiB
   /dev/mapper/luks3       1.00GiB
   /dev/sdd    3.00GiB
```

mount the pool as degraded
--------------------------

You can add in the real mirror device(s) later:

*Change _x_ to match the device.*

`mount -odegraded /dev/sdx /mnt/btrfs-pool`

add devices to pool
-------------------

*Change _x1_ to match the device.*

`btrfs dev add /dev/sdx1 /mnt/btrfs-pool`

Scan for btfrs filesystems
--------------------------

Scan devices for a btrfs filesystem and register them.

`btrfs device scan`

Create a subvolume
------------------

*Change _tmp_ to match the device.*

`btrfs subvolume create /mnt/btrfs-pool/tmp`

then add to `/etc/fstab` similar to any normal mount, eg:

```
# <file system>     <mount point>   <type>  <options>                                            <dump> <pass>
LABEL=btrfs-pool    /mnt/tmp        btrfs   defaults,nodev,nosuid,noexec,compress=lzo,subvol=tmp 0      2
```

Balance
-------

Balance quietly:

*The balance command without filters will basically rewrite everything
in the filesystem. The run time is potentially very long.*

`btrfs balance start /mnt/btrfs-pool`

Balance and be verbose:

`btrfs balance start -v /mnt/btrfs-pool`

Check the status of a balance:

`btrfs balance status -v /mnt/btrfs-pool`

Only balance block groups with usage under the given percentage (in this
example it's 70%):

`btrfs balance start -dusage=70 -musage=70 /mnt/btrfs-pool`

Resize
------

### Resize to max

Resize the whole pool:

`btrfs filesystem resize max /mnt/btrfs-pool`

or just resize individual devices:

```
btrfs filesystem resize 1:max /mnt/btrfs-pool
btrfs filesystem resize 2:max /mnt/btrfs-pool
btrfs filesystem resize 3:max /mnt/btrfs-pool
btrfs filesystem resize 5:max /mnt/btrfs-pool
```

### Reduce by a bit

*Change _<devid>_ to match the device.*

`btrfs filesystem resize <devid>:-xM /mnt/btrfs-pool`

Delete
------

### Delete an id

*Change _x_ to match the device.*

`sudo btrfs device delete /dev/mapper/luksx /mnt/btrfs-pool`