On Wed, Apr 23, 2014 at 05:04:10PM -0400, Sergey Ivanyuk wrote: > Hi, > > I have a filesystem that I've converted to raid6 from raid1, on 4 drives (I > have another copy of the data): > > Total devices 4 FS bytes used 924.64GiB > devid 1 size 1.82TiB used 474.00GiB path /dev/sdd > devid 2 size 465.76GiB used 465.76GiB path /dev/sda > devid 3 size 465.76GiB used 465.76GiB path /dev/sdb > devid 4 size 465.76GiB used 465.73GiB path /dev/sdc > > Data, RAID6: total=924.00GiB, used=923.42GiB > System, RAID1: total=32.00MiB, used=208.00KiB > Metadata, RAID1: total=1.70GiB, used=1.28GiB > Metadata, DUP: total=384.00MiB, used=252.13MiB > unknown, single: total=512.00MiB, used=0.00 > > > Recent btrfs-progs built from source, kernel 3.15.0-rc2 on armv7l. Despite > having plenty of space left on the larger drive, attempting to copy more > data onto the filesystem results in a kworker process pegged at 100% CPU > for a very long time (10s of minutes), at which point the writes proceed > for some time, and the process repeats until the eventual "No space left on > device" error. Balancing fails with the same error, even if attempting to > convert back to raid1. > > I realize that this likely has something to do with the disparity between > device sizes, and per the wiki a fixed-width stripe may help, though I'm > not sure if it's possible to change the stripe width in my situation, since > I can't rebalance. Is there anything I can do to get this filesystem back > to writable state?
With those device sizes, yes, you're going to have limits on the available data you can store -- with RAID-6, it'll be 465.76*(4-2) = 931.52 GB (less metadata space), so your conclusion above is indeed correct. We don't have the fixed-width stripe feature implemented yet, which probably explains why you can't use it. :) You can play with an approximation of the consequences, once the feature is there, at http://carfax.org.uk/btrfs-usage/ . Without that feature, though, there's not much you can do to improve the situation. What might help in converting back to RAID-1 is adding a small device to the FS temporarily before doing the conversion, and then removing it again afterwards. > Also, here's a stack trace for the stuck kworker process, which appears to > be a bug since it does this for a very long time: This is probably something different. Hugo. -- === Hugo Mills: hugo@... carfax.org.uk | darksatanic.net | lug.org.uk === PGP key: 65E74AC0 from wwwkeys.eu.pgp.net or http://www.carfax.org.uk --- Computer Science is not about computers, any more than --- astronomy is about telescopes.
signature.asc
Description: Digital signature
