linux-kernel - Re: very poor ext3 write performance on big filesystems?

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Message-ID: <47C9B6CD.3040709@tmr.com>
Date:	Sat, 01 Mar 2008 15:04:29 -0500
From:	Bill Davidsen <davidsen@....com>
To:	Andreas Dilger <adilger@....COM>
CC:	Tomasz Chmielewski <mangoo@...g.org>, Theodore Tso <tytso@....edu>,
	Andi Kleen <andi@...stfloor.org>,
	LKML <linux-fsdevel@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>, linux-raid@...r.kernel.org
Subject: Re: very poor ext3 write performance on big filesystems?

Andreas Dilger wrote:
> I'm CCing the linux-raid mailing list, since I suspect they will be
> interested in this result.
>
> I would suspect that the "journal guided RAID recovery" mechanism
> developed by U.Wisconsin may significantly benefit this workload
> because the filesystem journal is already recording all of these
> block numbers and the MD bitmap mechanism is pure overhead.
>   

Thanks for sharing these numbers. I think use of a bitmap is one of 
those things which people have to configure to match their use, 
certainly using a larger bitmap seems to reduce the delays, using an 
external bitmap certainly help, especially on an SSD. But on a large 
array, without a bitmap, performance can be compromised for hours during 
recovery, so the administrator must decide if normal case performance is 
more important than worst case performance.

-- 
Bill Davidsen <davidsen@....com>
  "Woe unto the statesman who makes war without a reason that will still
  be valid when the war is over..." Otto von Bismark 


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