I've got 4 drives in my server: sd{a,b,c,d}. All of them are in a raid1 system.

2 of those drives, sd{b,c} are completely empty. RAID1 will only make one copy of a file on a different drive. So it doesn't even make sense to have 4 harddrives in a single RAID1 system.

What I want to do is remove sd{b,c} from the btrfs system and install btrfs on each of those drives.

Then I want to move 2 of my 3 subvolumes from the original btrfs system onto those new two.

And then I'd like to remove the RAID1 from the original btrfs system, so that I can use the other disk for backups.

  • Are you using Btrfs RAID1 or mdadm RAID1 or something else? If you are using Btrfs RAID1 (across 4 disks) then you should definitely expect better balancing than 2 full disks and 2 empty disks. Did you add the two empty disks afterwards? If so then you can do a Btrfs rebalance to get it to move data to those disks. Maybe your question would be clearer if it contained the output of btrfs fi show. – Celada Jun 29 '15 at 2:21

Despite the RAID problem, you could use

btrfs send /source-volume/subvolume | btrfs receive /destination-volume

to copy subvolumes.

Manpage btrfs-send

Manpage btrfs-receive

For the actual RAID-problem you could see:

Manpage btrfs-balance

  • I'll give it a try – Harrys Kavan Jun 29 '15 at 19:45
  • And see the -p option of btrfs-send. – Jodka Lemon Jun 30 '15 at 13:21

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