BTRFS RAID1 and how to fix it


I mentioned in my previous post that I use an external drive to keep my Steam games on. In an attempt to not have to re-download hundreds of gigabytes of games I keep them on a RAID1 with 2x5TB drives that I use BTRFS to manage. In this post I’m going to outline how I set it all up, and how I manage it when issues arise.

First of all I had to format the drives, so I made sure they were empty and everything was backed up. Don’t do this unless you know for sure that all the data on all your drives is backed up somewhere else, or you want to delete it permanently.

Okay so the commands are easy, you just have to make sure you’re using the right ones as not to lose your data. Don’t run these commands without understanding what they do. Replace _ with your drive letter. A lot of these commands need to be run with root, make sure to either elevate to root (sudo -s) or prepend the commands with sudo.

mkfs.btrfs /dev/sd_1
mkfs.btrfs /dev/sd_1

Now you can mount the newly formatted drives to a single RAID1.

mount /dev/sd_1 /mnt
btrfs device add /dev/sd_1 /mnt
btrfs balance start -dconvert=raid1 -mconvert=raid1 /mnt

The last command might take a little bit of time, but once it’s finished your drives will be all ready to be used.

Now if you need to swap out a drive, add another, or you unplug one when it’s writing you can simply balance again and btrfs should be able to balance back onto the drive.

btrfs balance start -dconvert=raid1 -mconvert=raid1 /mnt

You can view the status of the balance using:

btrfs balance status

You can remove a drive or add another using:

btrfs device remove /dev/sd_1
btrfs device add /dev/sd_1

Just make sure you balance right afterwards (which will take a VERY long time if you have lots of data, beware)

btrfs balance start -dconvert=raid1 -mconvert=raid1 /mnt