BTRFS RAID1 and how to fix it

BTRFS RAID1 Setup

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.

Formatting Drives

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.

lsblk

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

Creating the RAID1 Array

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.

Managing the Array

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