From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alexander Koch Subject: btrfs-raid10 <-> btrfs-raid1 confusion Date: Sun, 06 May 2012 16:48:48 +0200 Message-ID: <4FA68F50.60505@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15 To: linux-btrfs@vger.kernel.org Return-path: List-ID: Greetings, until yesterday I was running a btrfs filesystem across two 2.0 TiB disks in RAID1 mode for both metadata and data without any problems. As space was getting short I wanted to extend the filesystem by two additional drives lying around, which both are 1.0 TiB in size. Knowing little about the btrfs RAID implementation I thought I had to switch to RAID10 mode, which I was told is currently not possible (and later found out that it is indeed). Then I read this [1] mailing list post basically saying that, in the special case of four disks, btrfs-raid1 behaves exactly like RAID10. So I added the two new disks to my existing filesystem $ btrfs device add /dev/sde1 /dev/sdf1 /mnt/archive and as the capacity reported by 'btrfs filesystem df' did not increase, I started a balancing run: $ btrfs filesystem balance start /mnt/archive Waiting for the balancing run to finish (which will take much longer than I thought; still running) I found out that as of kernel 3.3 changing the RAID level (aka restriping) is now possible: [2]. I got two questions now: 1.) Is there really no difference between btrfs-raid1 and btrfs-raid10 in my case (2 x 2TiB, 2 x 1TiB disks)? Same degree of fault tolerance? 2.) Summing up the capacities reported by 'btrfs filesystem df' I only get ~2.25 TiB for my filesystem, is that a realistic net size for 3 TiB gross? $ btrfs filesystem df /mnt/archive Data, RAID1: total=2.10TB, used=1.68TB Data: total=8.00MB, used=0.00 System, RAID1: total=40.00MB, used=324.00KB System: total=4.00MB, used=0.00 Metadata, RAID1: total=112.50GB, used=3.21GB Metadata: total=8.00MB, used=0.00 Thanks in advance for any advice! Regards, lynix [1] http://www.spinics.net/lists/linux-btrfs/msg15867.html [2] https://lkml.org/lkml/2012/1/17/381