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Date:      Thu, 29 Mar 2007 14:42:32 +0200
From:      Ivan Voras <ivoras@fer.hr>
To:        freebsd-geom@freebsd.org
Subject:   Re: raid3 is slow
Message-ID:  <eugc7p$kmh$1@sea.gmane.org>
In-Reply-To: <007c01c771fe$805b2fc0$6502a8c0@peteruj>
References:  <003401c7712a$f71ebb60$6502a8c0@peteruj><eudlg8$pm4$1@sea.gmane.org>	<005c01c77134$28e0fce0$6502a8c0@peteruj><86zm5xph7o.fsf@dwp.des.no>	<005301c771e4$bb0a3900$6502a8c0@peteruj>	<86lkhg5oz5.fsf@dwp.des.no> <007c01c771fe$805b2fc0$6502a8c0@peteruj>

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Szab=C3=B3 P=C3=A9ter wrote:

>>> After a few minutes

>  PID USERNAME  THR PRI NICE   SIZE    RES STATE    TIME   WCPU COMMAND
>    4 root        1  -8    0     0K     8K -       42:47 53.27% g_down
> 15400 root        1  -8    0     0K     8K -       82:18 19.38% g_bde=20
> raid3/nmivole
>   11 root        1 171   52     0K     8K RUN    968:44 12.60% idle
>    3 root        1  -8    0     0K     8K -       22:12  3.03% g_up
> 19970 root        1 -16    0  3400K  1772K wdrain   1:12  2.93% dd
>   40 root        1  -8    0     0K     8K r3:w1   36:18  1.07% g_raid3 =

> nmivol

> It seems terible!!! g_down gets more and more and more WCPU, and the=20
> load goes to the skies. I don't know, what should i think. Now i can=20
> see, at the end i will change the raid3 to stripe ;) But i don't want t=
o :(

Also one of the "shouldn't happen" things - g_down is (roughly) the=20
kernel thread that dispatches IO requests from the file system to the=20
lower level devices, gbde and graid3 in your case. It's strange that it=20
consumes that much CPU - it may mean that one of the GEOM classes is=20
being unusually slow in offloading requests to its own thread, or that=20
there's an unusual number of small requests bouncing between them. Try=20
running 'gstat' during this test and post some results.

If you have the time, also try using geli instead of gbde, just to=20
experiment.


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