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From: Mark Lord <liml@rtr.ca>
To: Jody McIntyre <scjody@sun.com>
Cc: Grant Grundler <grundler@google.com>, linux-ide@vger.kernel.org
Subject: Re: sata_mv performance; impact of NCQ
Date: Mon, 28 Apr 2008 13:41:13 -0400	[thread overview]
Message-ID: <48160C39.6000701@rtr.ca> (raw)
In-Reply-To: <20080428171449.GI17369@modernduck.com>

Jody McIntyre wrote:
>
> We turn write caching off for data integrity reasons (write reordering
> does bad things to journalling file systems if power is interrupted -
> and at the scale of many Lustre deployments, it happens often enough to
> be a concern.)  I'm also concerned about the effects of NCQ in this area
> so we'll probably turn it off anyway.
..

I haven't done a detailed examination lately, but..

Both write-caching and NCQ re-ordering should be safe on Linux.
The kernel will issue FLUSH_CACHE_EXT commands as required to checkpoint
data to the disk.

Or at least that's how I understood Tejun's last explanation of it.
It is possible that the drive firmware in some brands may not follow
spec for FLUSH_CACHE_EXT, but I don't know of a specific instance of this.

Cheers

  reply	other threads:[~2008-04-28 17:41 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-04-26  0:16 sata_mv performance; impact of NCQ Jody McIntyre
2008-04-26  3:13 ` Grant Grundler
2008-04-28 17:14   ` Jody McIntyre
2008-04-28 17:41     ` Mark Lord [this message]
2008-04-28 17:53       ` Alan Cox
2008-04-28 20:07       ` Jeff Garzik
2008-04-26  4:49 ` Mark Lord
2008-04-28 17:33   ` Jody McIntyre

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