"High" cpu usage when using ZFS cache device
Alexander at Leidinger.net
Tue Nov 16 16:31:33 UTC 2010
Quoting Christer Solskogen <christer.solskogen at gmail.com> (from Tue,
16 Nov 2010 14:00:48 +0100):
> On Tue, Nov 16, 2010 at 1:55 PM, Alexander Leidinger
> <Alexander at leidinger.net> wrote:
>> How do you measure that nothing is read or written to it?
> I used zpool iostat -v
"zpool iostat" (without -v) does not show cache filling writes to the
cache device. I do not know about -v, but I would not be surprised if
it does not show this too.
>> Please check with
>> gstat -f '^<DEVICE>$'
>> if there are really no reads/writes to the device (please replace <DEVICE>
>> with the name of your USB device, e.g. da0).
>> If you see writes, I would say
>> - this is the reason for the load
>> - your cache is on the way to be filled with
>> useful data
> I see almost no writes (nor reads)
I'm not sure: you verified the output of "zpool iostat -v" with gstat
or not? If not, please do.
>> If gstat shows zero activity, I suggest to run 'top -S' and look at the
>> process(es) which consume about 10% CPU (do not take care about the idle
>> process). Based upon this we can maybe suggest further things to
> Heres the output of that:
> CPU: 0.0% user, 0.0% nice, 11.8% system, 0.0% interrupt, 88.1% idle
> Mem: 841M Active, 193M Inact, 5086M Wired, 4876K Cache, 1237M Buf, 5750M Free
> Swap: 8192M Total, 8192M Free
> PID USERNAME THR PRI NICE SIZE RES STATE C TIME WCPU COMMAND
> 11 root 8 171 ki31 0K 128K CPU0 0 ??? 713.62% idle
> 5 root 5 -8 - 0K 76K zvol:i 5 401.9H 91.16% zfskern
> Thanks for your time on looking into this :-)
Based upon you other answer (with -H), I would still think the L2arc
(cache) device is being filled in the background (which means there
should be something visible with gstat).
Sorry never means having you're say to love.
http://www.Leidinger.net Alexander @ Leidinger.net: PGP ID = B0063FE7
http://www.FreeBSD.org netchild @ FreeBSD.org : PGP ID = 72077137
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