BTRFS

See also

• Using Btrfs with Multiple Devices - btrfs Wiki 1

• Btrfs - ArchWiki 2

• Btrfs/Checksum Algorithms - Forza’s ramblings 3

RAID

Commands

These examples assume that a RAID 1 BTRFS array (not BTRFS over mdadm RAID) is mounted on /data.

Note

After creating, adding or removing devices from an array always run the balance operation. You may want to use GNU screen to put the process in background, like this

apt-get install screen
screen btrfs balance start /data

Create

1. crate the array

   mkfs.btrfs --csum xxhash -m raid1 -d raid1 /dev/sda1 /dev/sdb1
   

2. mount normally

   mount /dev/sdb1 /data
   

3. To add new partitions, for example /dev/sdc1 and /dev/sdd1, run

   btrfs device add /dev/sdc1 /dev/sdd1 /data
   

4. run the balance operation

Removing devices

1. remove two devices at the same time

   btrfs device delete /dev/sdc1 /dev/sdd1 /data
   

2. run the balance operation

Replace a device

1. replace /dev/old with /dev/new. This operation should run in background

   btrfs replace start /dev/old /dev/new /data
   

2. check

   btrfs replace status /data
   

Convert metadata profile

You can clone partitions with dd from HDDs to SSDs. After that run:

screen btrfs balance start -v -mconvert=single /data

Check usage

btrfs filesystem usage /data
btrfs filesystem df /data

Footnotes

1

https://btrfs.wiki.kernel.org/index.php/Using_Btrfs_with_Multiple_Devices unknown license

2

https://wiki.archlinux.org/index.php/Btrfs GNU Free Documentation License 1.3 or later, Copyright (c) ArchWiki contributors

3

https://wiki.tnonline.net/w/Btrfs/Checksum_Algorithms CC-BY-SA 4.0, Copyright (c) Forza’s ramblings