Poor performance solved WAS: Re: [DRBD-user] 2.6.24-rc1 oops

Lars Ellenberg lars.ellenberg at linbit.com
Sun Nov 11 16:13:29 CET 2007

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.

On Sat, Nov 10, 2007 at 02:10:39AM +0100, Matteo Tescione wrote:
> Leroy, drbd folks,
> After a while of collecting and profiling my systems i discovered that our
> poor performance problems were not related of processor, raid controller or
> kernel configuration.
> It's all about raid5/6 level configurations that is absolutely unreliable.
> In details reading and writing directly to the raid disk, with an ext3
> partition for example, gives more than 200 mbyte/sec with await and svc time
> of approx 1.2 ms versus reading and writing with drbd (either syncing or
> live i/o) gives extremely poor performance (i got 30-40 mbyte/sec with 3ware
> 9650-8p configured in raid6 and i have 20 mbytes/sec with Compaq Smart Array
> p400 configured in raid5 mode.
> In both raid5/6 configurations, i/o seems stucked as i've reported in my
> previous post with very high iowait values (await up to 5000 ms, svctime up
> to 1000 ms)
> Switching to raid0 / raid10 configurations, totally solved our problems.
> Sync its up to 200mbyte/sec, live i/o seems good as well but i'm still
> testing the vmware infrastructure...
> If anyone has any idea of what's going on....

try to put the drbd meta data on a raid1,
and leave the data area on raid5 or 6.

my guess is that the latency of a synchonous sector write
in a raid5/6 set is too high.

: Lars Ellenberg                            Tel +43-1-8178292-55 :
: LINBIT Information Technologies GmbH      Fax +43-1-8178292-82 :
: Vivenotgasse 48, A-1120 Vienna/Europe    http://www.linbit.com :

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