Machine stops for some seconds with ZFS

Attila Nagy bra at fsn.hu
Wed Feb 3 12:48:33 UTC 2010


Tommi Lätti wrote:
>> I'm not sure about these are being the same. When I see these "stops",
>> nothing happens. gstat shows no IO, and everything goes very quiet for some
>> painful (10s of) seconds. Also, buildworld doesn't do too heavy IO, at least
>> for these drives.
>>     
>
> Well that's what I experienced. iostat says 0, machine is kind of
> responsive, unless you try to read or write from the zfs pool..
>   
Oh, that wasn't clear to me, so you are also experiencing a total 
blackout in disk IO.
I'm not sure how this could be traced.
>   
>> BTW, we are doing tests in a completely different environment with ZFS and
>> NFS (15k drives, with BBWC), and it seems something similar happens there
>> too, resulting in a freeze in the end.
>>     
>>> Combine with 5400 rpm consumer drives... well...
>>>
>>>       
>> Doesn't really count, but these drives are 7k2.
>>     
>
> If it's a zfs arc problem it would definitely manifest on 15k drives
> too, what I meant that the impact might be unnoticeable. But since I
> don't have a nice SAN to test with right now I can't try it out with
> 100+ disks.
>   
I'm still not getting the point. If you see zero IO during the problem, 
how would a faster storage make impact on its visibility?


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