linux-kernel - Re: 2.6.20: stripe_cache

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Date:	Fri, 23 Feb 2007 22:41:00 +1000
From:	Jason Rainforest <l3mming@...et.net.au>
To:	Justin Piszcz <jpiszcz@...idpixels.com>
Cc:	linux-kernel@...r.kernel.org, linux-raid@...r.kernel.org
Subject: Re: 2.6.20: stripe_cache_size goes boom with 32mb

Hi Justin,

I'm not a RAID or kernel developer, but .. do you have enough RAM to
support a 32mb stripe_cache_size?! Here on my 7*250Gb SW RAID5 array,
decreasing a stripe_cache_size of 8192 to 4096 frees up no less than
120mb of RAM. Using that as a calculation tool, a 32mb stripe_cache_size
would require approximately 960mb of RAM! My RAID box only has 1Gb of
RAM, so I'm not game to test such a thing. Others on these lists would
definitely have a good idea on what's happening :-)

Cheers,
Jason


On Fri, 2007-02-23 at 06:41 -0500, Justin Piszcz wrote:
> Each of these are averaged over three runs with 6 SATA disks in a SW RAID 
> 5 configuration:
> 
> (dd if=/dev/zero of=file_1 bs=1M count=2000)
> 
> 128k_stripe: 69.2MB/s
> 256k_stripe: 105.3MB/s
> 512k_stripe: 142.0MB/s
> 1024k_stripe: 144.6MB/s
> 2048k_stripe: 208.3MB/s
> 4096k_stripe: 223.6MB/s
> 8192k_stripe: 226.0MB/s
> 16384k_stripe: 215.0MB/s
> 
> When I tried a 32768k stripe, this happened:
> p34:~# echo 32768 > /sys/block/md4/md/stripe_cache_size
> Connection to p34 closed
> 
> I was able to Alt-SysRQ+b but I could not access the console/X/etc, it 
> appeared to be frozen.
> 
> FYI.
> 
> Justin.
> 
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