slowdown of zfs (tx->tx)

[Artem Belevich]

On Fri, Jan 18, 2013 at 3:26 AM, Nicolas Rachinsky
<fbsd-mas-0 at ml.turing-complete.org> wrote:
> * Artem Belevich <art at freebsd.org> [2013-01-16 00:45 -0800]:
>> On Tue, Jan 15, 2013 at 11:37 PM, Nicolas Rachinsky
>> <fbsd-mas-0 at ml.turing-complete.org> wrote:
>> >> You may want to update your system to very recent FreeBSD as quite a
>> >> few fixes were recently imported from illumos. Hopefully it will deal
>> >> with the issue. I'm out of ideas otherwise. Sorry.
>> >
>> > Do you mean -CURRENT or -STABLE with very recent? Or just 9.1?
>>
>> -HEAD or -STABLE (-8 or -9).
>
> I have now updated the machine to stable/8 r245541. I have not updated
> the zpool.
>
> But the problem still occurs. Should I update the pool? Or try other
> things first?

 Updating the pool is an irreversible operation. In general I'd
suggest trying less drastic options first.

Other people suggested that the problem may be just a side effect of
almost-full filesystem. ZFS needs fair amount of unfragmented free
space in order to work efficiently. If that's what's causing your
problem, then one thing to try would be to free enough free space. The
gotcha there is that you need to free up enough contiguous space.
Removing bunch of recently written files may not help as those writes
would happen on already fragmented FS. Removing files written when FS
had a lot of free space may have better chance of freeing contiguous
space. Old snapshots are good candidates for this.

Other than that I'm out of ideas. Sorry.

--Artem