Thanks, this makes sense. I freed up some space and the re-balance back to raid1 is now running (I had to run 'btrfs balance -dusage=5' before some free space actually became available).
Filed the other issue as https://bugzilla.kernel.org/show_bug.cgi?id=74761 . On Wed, Apr 23, 2014 at 6:53 PM, Hugo Mills <h...@carfax.org.uk> wrote: > 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. -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
