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

To: Arkadiusz MiÅkiewicz <arekm@xxxxxxxx>
Subject: Re: md-RAID5/6 stripe_cache_size default value vs performance vs memory footprint
From: Stan Hoeppner <stan@xxxxxxxxxxxxxxxxx>
Date: Sat, 21 Dec 2013 19:41:37 -0600
Cc: 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>
Reply-to: stan@xxxxxxxxxxxxxxxxx
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On 12/21/2013 5:18 AM, Stan Hoeppner wrote:
...
> For example, I assisted a user with 5x Intel SSDs back in January and
> his system required 4096, or 80MB of RAM for stripe cache, to reach
> maximum write throughput of the devices.  This yielded 600MB/s or 60%
> greater throughput than 2048, or 40MB RAM for cache.  In his case 60MB
> more RAM than the default was well worth the increase as the machine was
> an iSCSI target server with 8GB RAM.

Correction here.  I said above that 80MB was 60MB greater than the
default for his 5 drives.  This should have said 75MB greater than the
default which is 1MB per member device, or 5MB for 5 drives.

-- 
Stan

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