slowdown of zfs (tx->tx)

[Artem Belevich]

On Thu, Jan 10, 2013 at 11:34 PM, Nicolas Rachinsky
<fbsd-mas-0 at ml.turing-complete.org> wrote:
> * Nicolas Rachinsky <fbsd-mas-0 at ml.turing-complete.org> [2013-01-10 20:39 +0100]:
>> after replacing one of the controllers, all problems seem to have
>> disappeared. Thank you very much for your advice!
>
> Now the problem is back.
>
> After changing the controller, there were no more timeouts logged.
>
> No UDMA_CRC_Error_Count changed.
>

Is there anything special about ada8? It does seem to have noticeably
higher service time compared to other disks.

Cound you do gstat with 1-second interval. Some of the 5-second
samples show that ada8 is the bottleneck -- it has its request queue
full (L(q)=10) when all other drives were done with their jobs. And
that's a 5-sec average. Its write service time also seems to be a lot
higher than for other drives.

Does the drive have its write cache disabled by any chance? That could
explain why it takes so much longer to service writes.

Can you remove ada8 and see if your performance go back to normal?

--Artem