Re: Bad fs performance, IO freezes

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Accidentally didn't reply to the list the 1st time.

I see the same issue when I have quotas enabled.  If you have quotas
on, see if turning them off helps.

On Mon, Oct 26, 2015 at 7:16 AM, cheater00 . <cheater00@xxxxxxxxx> wrote:
> Hi guys,
> I am running into really bad performance. Here's my setup:
>
> WD Red 6 TB connected over USB2 to my core i7 laptop, running Ubuntu
> 32-bit with kernel 4.0.4-040004-generic #201505171336.
>
> Single btrfs partition covering whole disk.
>
> Autodefrag is on.
>
> fstab line:
> UUID=... /media/X btrfs rw,nosuid,nodev,autodefrag 0 0
>
> Sometimes when files are being modified or removed, I see
> btrfs-transacti eat 100% cpu; during this time no io operations
> succeed, that is, they're all stalled. You can't even ls on that fs.
> This happens for several minutes then normal operation resumes. There
> doesn't seem to be a rule to what will trigger this, other than
> opening a single file and reading usually works quite well. (say,
> watching a movie while all other programs are closed). But even moving
> files off the disks triggers some sort of bug. Just now I am moving a
> few files (just 30gb worth) onto another disk, and the bug triggers.
> So btrfs-transacti was eating my cpu for over 5 minutes and according
> to mv's output after this was done and cpu usage went back to normal
> what I was waiting for was for a tiny png file to be removed. This is
> pretty bad.
>
> I have tried defragmenting directories where files are being accessed
> and moved. This hasn't helped.
>
> This happens whether the FS is near full or not. It currently is near
> full but it wasn't before and it still did that. It still has about ~
> 100GB free space now.
>
> The more things are happening the more often this bug gets triggered.
> So if I have utorrent running and its temporary downloads directory is
> there, its download speed graph will be a few spikes of running at
> several MB/sec separated by durations of 0 download speed.
>
> Nothing seems to show up in dmesg or syslog.
>
> I have asked in #btrfs but the suggestions ended up not fixing the
> issue (autodefrag, defrag dirs).
>
> Please advise what I should do with this issue.
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