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Date:      Thu, 29 Jan 2009 15:56:54 +0000
From:      Richard Tector <richardtector@thekeelecentre.com>
To:        "Peter C. Lai" <peter@simons-rock.edu>
Cc:        Charles Sprickman <spork@bway.net>, freebsd-stable@freebsd.org
Subject:   Re: 7.1, mpt and slow writes
Message-ID:  <4981D1C6.6070605@thekeelecentre.com>
In-Reply-To: <20090129154828.GC63236@cesium.hyperfine.info>
References:  <alpine.OSX.2.00.0901290351250.37588@toasty.nat.fasttrackmonkey.com> <49819672.1090208@thekeelecentre.com> <20090129154828.GC63236@cesium.hyperfine.info>
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[-- Attachment #1 --]
Peter C. Lai wrote:
> I am guessing this is only related to SATA drives on SAS controllers?
> The only mpt hardware I have is LSILogic 1030 Ultra4 and it writes
> sustained 40MB/s to my LTO-2 drives out of the box without any tweaking.

Correct. When SATA drives are used instead of SAS drives on this 
controller it disables the write cache resulting in poor performance.
The tunable was added by Scott Long to solve the problem (though at the 
cost of greater risk to data).

Richard

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