From: Jeff Garzik <jeff@garzik.org>
To: Mark Lord <liml@rtr.ca>
Cc: Jody McIntyre <scjody@sun.com>,
Grant Grundler <grundler@google.com>,
linux-ide@vger.kernel.org
Subject: Re: sata_mv performance; impact of NCQ
Date: Mon, 28 Apr 2008 16:07:55 -0400 [thread overview]
Message-ID: <48162E9B.2030400@garzik.org> (raw)
In-Reply-To: <48160C39.6000701@rtr.ca>
Mark Lord wrote:
> 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.
It depends on the fs's use of barriers (or not).
Without barriers, FLUSH CACHE[ EXT] isn't issued very often.
Jeff
next prev parent reply other threads:[~2008-04-28 20:08 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
2008-04-28 17:53 ` Alan Cox
2008-04-28 20:07 ` Jeff Garzik [this message]
2008-04-26 4:49 ` Mark Lord
2008-04-28 17:33 ` Jody McIntyre
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