Date: Mon, 1 Nov 2004 00:26:57 +0100 From: Brad Knowles <brad@stop.mail-abuse.org> To: <freebsd@newmillennium.net.au> Cc: freebsd-current@freebsd.org Subject: Re: Gvinum RAID5 performance Message-ID: <p06002002bdab24905ad8@[10.0.1.3]> In-Reply-To: <002401c4bf9c$c4fee8e0$0201000a@riker> References: <002401c4bf9c$c4fee8e0$0201000a@riker>
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At 9:55 AM +1100 2004-11-01, <freebsd@newmillennium.net.au> wrote:
> Now, running a dd from a plex gives me less performance than running a
> dd from one of the subdisks, even though the array is not running in
> degraded mode.
Right. This is RAID-5. It is used for reliability, not
performance. The entire stripe has to be read at once and written at
once, for any operation involving that stripe.
If you want maximum performance, try RAID 1+0 (make sure to
stripe the mirrors and not mirror the stripes).
> On a final note, I'd like to implement the ability to grow RAID5 plexes
> - any suggestions on where to start?
This is a more complex issue than you realize. If you want to
contribute code to perform this operation, I'm sure that the project
would be more than happy to receive them in consideration for
inclusion in the gvinum code.
--
Brad Knowles, <brad@stop.mail-abuse.org>
"Those who would give up essential Liberty, to purchase a little
temporary Safety, deserve neither Liberty nor Safety."
-- Benjamin Franklin (1706-1790), reply of the Pennsylvania
Assembly to the Governor, November 11, 1755
SAGE member since 1995. See <http://www.sage.org/>; for more info.
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