From: "Jakob Østergaard" <jakob@unthought.net>
To: Bernd Eckenfels <ecki-news2002-04@lina.inka.de>
Cc: linux-kernel@vger.kernel.org
Subject: Re: raid1 performance
Date: Thu, 2 May 2002 18:37:58 +0200 [thread overview]
Message-ID: <20020502183758.Q31556@unthought.net> (raw)
In-Reply-To: <20020501130127.A10936@borg.org> <E1731ZL-0005Bl-00@sites.inka.de>
On Wed, May 01, 2002 at 11:23:23PM +0200, Bernd Eckenfels wrote:
> In article <20020501130127.A10936@borg.org> you wrote:
> > 1. Does the OS even know where the heads are in a modern IDE disk?
>
> > 2. Is "closer" any more finely grained than a binary
> > positioned/not-positioned?
>
> > And I guess another question: How much does RAID 1 help and under what
> > kinds of usage?
>
> No, you just distribute the ready round robin, this means each disk has only
> half the seeks it had before.
No, this is the way it was done a long time ago.
It turns out to be an incredibly bad idea. In fact, it is the most CPU-efficient
way of guaranteeing the largest average seek times on your disks ;)
The RAID-1 code now looks at which disk worked closest to the wanted position
last, and picks that disk for the seek.
> As long as you do not spread continous blocks
> (readahead) stats are good you actually reduce overall seeks. This helps
> actually even if no seek is involved because of the fact that you need to
> wait for the begin of a track to read it.
The "new" code (which is not that new anymore) will allow one disk to keep
on a single sequential read for a long time (eventually it will kick in the
idle disk(s) though).
--
................................................................
: jakob@unthought.net : And I see the elder races, :
:.........................: putrid forms of man :
: Jakob Østergaard : See him rise and claim the earth, :
: OZ9ABN : his downfall is at hand. :
:.........................:............{Konkhra}...............:
next prev parent reply other threads:[~2002-05-02 16:38 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-04-30 12:23 raid1 performance Jaime Medrano
2002-04-30 12:38 ` Arjan van de Ven
2002-04-30 14:21 ` Kent Borg
2002-05-01 16:35 ` Jakob Østergaard
2002-05-01 17:01 ` Kent Borg
2002-05-01 17:16 ` Justin Cormack
2002-05-01 21:23 ` Bernd Eckenfels
2002-05-02 16:37 ` Jakob Østergaard [this message]
2002-06-29 0:01 ` Bernd Eckenfels
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