linux-kernel - Re: [dm-devel] Re: [PATCH] Implement barrier support for single device DM devices

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Message-ID: <47BA8C27.6020108@msgid.tls.msk.ru>
Date:	Tue, 19 Feb 2008 10:58:31 +0300
From:	Michael Tokarev <mjt@....msk.ru>
To:	Jeremy Higdon <jeremy@....com>
CC:	David Chinner <dgc@....com>, Ric Wheeler <ric@....com>,
	device-mapper development <dm-devel@...hat.com>,
	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org
Subject: Re: [dm-devel] Re: [PATCH] Implement barrier support for single device
 DM devices

Jeremy Higdon wrote:
[]
> I'll put it even more strongly.  My experience is that disabling write
> cache plus disabling barriers is often much faster than enabling both
> barriers and write cache enabled, when doing metadata intensive
> operations, as long as you have a drive that is good at CTQ/NCQ.

Now, and it's VERY interesting at least for me (and is off-topic in
this thread) -- which drive(s) are good at NCQ?  I tried numerous SATA
(NCQ is about sata, right? :) drives, but NCQ either does nothing in
terms of performance or hurts.  Yesterday we ordered another drive
from Hitachi (their "raid edition" thing), -- will try it tomorrow,
but I've no hope here as it's some 5th or 6th model/brand already.

(Ol'good SCSI drives, even 10 years old, shows large difference when
TCQ is enabled...)

Thanks!
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