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Re: md-RAID5/6 stripe_cache_size default value vs performance vs memory

To: Stan Hoeppner <stan@xxxxxxxxxxxxxxxxx>
Subject: Re: md-RAID5/6 stripe_cache_size default value vs performance vs memory footprint
From: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Date: Thu, 26 Dec 2013 00:55:10 -0800
Cc: Arkadiusz Mi??kiewicz <arekm@xxxxxxxx>, linux-raid@xxxxxxxxxxxxxxx, "xfs@xxxxxxxxxxx" <xfs@xxxxxxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <52B57912.5080000@xxxxxxxxxxxxxxxxx>
References: <52B102FF.8040404@xxxxxxxxxxx> <52B2FE9E.50307@xxxxxxxxxxxxxxxxx> <52B41B67.9030308@xxxxxxxxxxx> <201312202343.47895.arekm@xxxxxxxx> <52B57912.5080000@xxxxxxxxxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Sat, Dec 21, 2013 at 05:18:42AM -0600, Stan Hoeppner wrote:
> The powers that be, Linus in particular, are not fond of default
> settings that create a lot of kernel memory structures.  The default
> md-RAID5/6 stripe_cache-size yields 1MB consumed per member device.

The default sizing is stupid as it basically makes RAID unusable out
of the box, I always have to fix that up, as well as a somewhat
reasonable chunk size for parity RAID to make it usable.  I'm also
pretty sure I complained about it at least once a while ago, but never
got a reply.

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