On 6/22/07, Jon Nelson [off-list ref] wrote:

On Thu, 21 Jun 2007, Raz wrote:

quoted

What is your raid configuration ?
Please note that the stripe_cache_size is acting as a bottle neck in some
cases.

Well, it's 3x SATA drives in raid5. 320G drives each, and I'm using a
314G partition from each disk (the rest of the space is quiescent).

what is the chunk size ?. Please note that a raid performance is dependent
on the access pattern to the disks. What is this raid aimed to do ?
more reads ? more writes ? If you can control the access pattern ,
you might be able to increase performance.

quoted

On 6/21/07, Jon Nelson [off-list ref] wrote:

quoted

I've been futzing with stripe_cache_size on a 3x component raid5,
using 2.6.18.8-0.3-default on x86_64 (openSUSE 10.2).

With the value set at 4096 I get pretty great write numbers.
2048 and on down the write numbers slowly drop.

However, at values above 512 the 'check' performance is terrible. By
'check' performance I mean the value displayed by /proc/mdstat after
I issue:

echo check > /sys/block/md0/md/sync_action

When I say "terrible" I mean < 3MB/s.
When I use 384, the performance goes to ~70MB/s
512.. 72-73MB/s
640.. 73-74MB/s

768.. 3300 K/s. Wow!

Can somebody 'splain to me what is going on?

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Jon Nelson [off-list ref]
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Raz

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Jon Nelson [off-list ref]
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Raz