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Re: Write caching, XFS log

To: Andrew Klaassen <ak@xxxxxxx>
Subject: Re: Write caching, XFS log
From: Andi Kleen <ak@xxxxxxx>
Date: Mon, 28 May 2001 23:05:23 +0200
Cc: linux-xfs@xxxxxxxxxxx
In-reply-to: <20010528111135.A3121@key.dkp.com>; from ak@dkp.com on Mon, May 28, 2001 at 11:11:35AM -0400
References: <20010528111135.A3121@key.dkp.com>
Sender: owner-linux-xfs@xxxxxxxxxxx
User-agent: Mutt/1.2.5i
On Mon, May 28, 2001 at 11:11:35AM -0400, Andrew Klaassen wrote:
> Question:  Would it make sense to put the XFS log on a device
> with write caching turned off, and the main portion of the file
> system on a device with write caching turned on?  From what I've
> been reading, turning on write caching can give a major
> performance boost in some cases, but can also seriously
> jeopardize metadata integrity, defeating the purpose of having a
> metadata-journalling FS in the first place.  Would turning off
> write caching just for the log get around this problem?

It won't, because XFS needs to know on the whole volume when a write
has finished; otherwise it could remove transactions from the log too 
early. A transaction can only be removed from the log when it has 
been safely comitted, and that's hard to find out with write caching.

-Andi

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