From: Mikael Abrahamsson <swmike@swm.pp.se>
To: Justin Piszcz <jpiszcz@lucidpixels.com>
Cc: Joshua Baker-LePain <jlb17@duke.edu>,
linux-ide-arrays@lists.math.uh.edu, linux-raid@vger.kernel.org
Subject: Re: 3ware 9650 tips
Date: Sat, 14 Jul 2007 11:04:13 +0200 (CEST) [thread overview]
Message-ID: <Pine.LNX.4.64.0707141100230.29164@uplift.swm.pp.se> (raw)
In-Reply-To: <Pine.LNX.4.64.0707131434470.31742@p34.internal.lan>
On Fri, 13 Jul 2007, Justin Piszcz wrote:
> You are using HW RAID then? Those numbers seem pretty awful for that
> setup, including linux-raid@ even it though it appears you're running HW
> raid, this is rather peculiar.
No, it has been discussed numerous times on this list.
SW raid is faster because it has access to (often) gigabytes of block
cache, which the HW raid controller doesn't have. SW raid is therefore
able to avoid a lot of reads when it needs to write, speeding things up
considerably.
I always use 3ware HW-raid though as I consider it more reliable. Since
most of my access is "write once, read many" write speed isn't as
important to me as data integrity.
Take your 3ware HW-raid, do a dd (read or write) to the device and see it
being very quick (because it can fit all the data into its cache as it
either reads or writes), then put a filesystem on it and do writes there,
especially journaled writes, and see write speed go down to 1/10 or so.
--
Mikael Abrahamsson email: swmike@swm.pp.se
next prev parent reply other threads:[~2007-07-14 9:04 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <alpine.LRH.0.999.0707131356520.25773@chaos.egr.duke.edu>
2007-07-13 18:35 ` 3ware 9650 tips Justin Piszcz
2007-07-13 18:54 ` Jon Collette
2007-07-13 19:36 ` Justin Piszcz
2007-07-16 2:41 ` David Chinner
2007-07-16 12:22 ` David Chinner
2007-07-16 12:39 ` Bernd Schubert
2007-07-16 15:50 ` Eric Sandeen
2007-07-16 22:21 ` David Chinner
2007-07-16 15:43 ` Joshua Baker-LePain
2007-07-16 17:15 ` [Advocacy] " Bryan J. Smith
2007-07-16 17:40 ` Al Boldi
2007-07-16 17:48 ` Matthew Wilcox
2007-07-16 18:28 ` [RFC] VFS: data=ordered (was: [Advocacy] Re: 3ware 9650 tips) Al Boldi
2007-07-16 19:02 ` Matthew Wilcox
2007-07-16 18:38 ` [Advocacy] Re: 3ware 9650 tips Bryan J. Smith
2007-07-16 17:34 ` Stuart Levy
2007-07-13 19:04 ` Joshua Baker-LePain
2007-07-13 23:30 ` Michael Tokarev
2007-07-14 1:23 ` Andrew Klaassen
2007-07-14 8:08 ` Justin Piszcz
2007-07-14 16:10 ` Andrew Klaassen
2007-07-14 16:11 ` Justin Piszcz
2007-07-14 16:14 ` Andrew Klaassen
2007-07-14 16:18 ` Justin Piszcz
2007-07-14 9:04 ` Mikael Abrahamsson [this message]
2007-07-14 16:11 ` Andrew Klaassen
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