In-place conversion of ext4 on RAID5 to btrfs RAID5

nemo19 · 18. März 2014

Hey everyone,

I'm fairly new to OMV and NAS in general and have a question concerning my storage setup.

I read quite a few things about btrfs recently and like the checksumming, CoW, and dynamic changing of RAID levels and array size. Afaik the next version of OMV in the not too distant future will support btrfs, since it will be based on wheezy. So once the new version is out I'd like to change my filesystem to btrfs using RAID5. I'd like to do the conversion in place, since I don't have that many spare disks and already know that ext4 can be converted to btrfs.

My question is how I should set up my storage now to make this possible. Am I right that I cannot use a RAID setup until then because btrfs does RAID inside the fs while the RAID currently offered by OMV is on a lower level? And running btrfs on top of it would get me checksumming but not automatic repair since btrfs would not not know of the redundant copy? And I also could not use btrfs' dynamic RAID features since it would only see the large RAID disk presented to it by OMV and not the individual drives and I'd have no change of changing that other than breaking the RAID and losing all data?

Thank you for your help

ryecoaaron · 18. März 2014

You can probably convert ext4 to btrfs that is still on top of mdadm software raid but I doubt you can convert ext4 on top of mdadm software raid to btrfs raid. I know you said you don't have the spare disks but I wouldn't want to try any of this without a backup.

From what I can tell, I doubt OMV will have support for btrfs raid 5 since it requires the backports kernel (and backports btrfs-tools). A ZFS plugin is being worked on.

davidh2k · 18. März 2014

Don't get your hopes to high with BTRFS. Even in Kernel 3.13 its still considered experimental!

Greetings
David

Gandalf1203 · 7. Januar 2015

Hi Folks,

Did anyone give it a try since BTRFS is now stable?

Right now Im in the middel of an btrfs-convert TEST EXT3 FS with 4x 2TB Raid5 MD devices and it takes ages to convert. 2 Days and only 170000000 from 700000000 inodes are converted by the tool.

Did anyone have the same experince while converting from ext3 to btrfs

Im using 3.16 bpo Kernel and the latst BTRFS Tools V3.18 from git.

subzero79 · 7. Januar 2015

Ext4 to btrfs in my rootfs. 8gb in like 30 minutes if I recall. I use btrfs in my data, but I've never though about converting it. I've brought one of the drives down from the raid1 and formatted then rsync it. Convert it to raid1 btrfs and balance the array.

Gandalf1203 · 8. Januar 2015

Thx for the answer

Okay your 8GB rootfs took 30 Minutes to convert right ?! Is your rootfs an SSD drive ?
So btrfs-convert is a slow beast.

Then the 5,8TB from the Raid5 will take approximately about 15 Days [when the "convert copy inode stuff" is linear]

Okay only 12 more to go then

subzero79 · 8. Januar 2015

Is an 2.5" sata1 or sata2 spin drive, can't recall. You can go to freenode #btrfs channel to ask.

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