Changing BTRFS RAID level

emphire · 2012-05-14 20:37:39

Linux 3.3 was supposed to have introduced support for re-striping between raid levels. Does anyone know how to go about doing so or know any good tutorials/documentation?

I'm thinking of getting a second drive, formatting it with btrfs, copying over my existing drive, and then adding the old drive and converting it to RAID1. If I can figure out how that is.

WorMzy · 2012-05-14 20:59:34

You may need btrfs-progs-git installed (not sure, but the information in the man pages doesn't correspond to the ability of the applications either way), but you can change raid levels using:

btrfs filesystem balance start -dconvert=<raidlevel> -mconvert=<raidlevel>

Remember to add the extra disk/partition to the btrfs partition first with

btrfs device add /dev/sd** /path/to/mounted/btrfsfilesystem

Make sure to backup any important data first, I've only done this once myself (converting raid1 to non-raid, since syslinux can't boot a multiple device btrfs partition apparently (even if it is just raid1))

emphire · 2012-05-15 19:58:37

Thanks WorMzy. I'll take the plunge and give it a try soon. I'm leaving a small ext2 boot partition for syslinux. Hopefully that will do the trick.

WorMzy · 2012-05-16 20:14:50

emphire wrote:

I'm leaving a small ext2 boot partition for syslinux. Hopefully that will do the trick.

...why didn't I think of that? Thanks in return for that.

WorMzy · 2012-05-18 16:05:23

*Shameless doublepost-bump*

If you got it working like that, mind letting me know how? Syslinux just seems to loop for me if /boot's on it's own partition. It doesn't even seem to attempt to load the kernel. Fortunately chainloading into grub still works, so I could boot my other installations and revert the changes, but I'd quite like to get this working.

cteampride · 2012-05-20 01:09:34

I am running a similar setup to your description. Yes, syslinux has a difficult time booting a raid1 btrfs array (it may be possible though?). I wound up giving up on syslinux and just using grub.

I left a small partition ext3 partition for grub on both my drives. grub-install <disk> works flawlessly this way. Technically, I dont think you need a dedicated /boot with grub now (as it now has full btrfs support?)

for both disks gdisk -l looks the same:

Number  Start (sector)    End (sector)  Size       Code  Name
   1            2048            6143   2.0 MiB     EF02  BIOS boot partition
   2            6144      1953523021   931.5 GiB   8300  Linux filesystem

I then created my btrfs raid1 array:

mkfs.btrfs -L TANK -d raid1 -m raid1 /dev/sda2 /dev/sdb2

grub-install went smoothly.

grub-install /dev/sda
grub-install /dev/sdb
grub-mkconfig -o /boot/grub/grub.cfg

MAKE sure you add the "btrfs" hook mkinitcpio to mkinitcpio.conf hooks array and regen your initramfs-linux.img. Somehow I forget to do this sometimes...

The resulting setup can be booted even if one drive fails (in degraded mode atleast). If a drive were to fail, its a little bit of a pain to setup the partitions on the failed drive replacement, add the device to the degraded btrfs, and install grub to it... but hey. Its relatively bullet proof: even more so with weekly snapshots and backups to a non-btrfs device.

Anyway I am really enjoying the btrfs features! good luck with the install.

Last edited by cteampride (2012-05-20 01:10:35)

Arch Linux

#1 2012-05-14 20:37:39

Changing BTRFS RAID level

#2 2012-05-14 20:59:34

Re: Changing BTRFS RAID level

#3 2012-05-15 19:58:37

Re: Changing BTRFS RAID level

#4 2012-05-16 20:14:50

Re: Changing BTRFS RAID level

#5 2012-05-18 16:05:23

Re: Changing BTRFS RAID level

#6 2012-05-20 01:09:34

Re: Changing BTRFS RAID level

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