From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Greaves <david@dgreaves.com>
Subject: Re: RAID-5 streaming read performance
Date: Wed, 13 Jul 2005 22:18:57 +0100
Message-ID: <42D58541.7000702@dgreaves.com>
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Cc: Dan Christensen <jdc@uwo.ca>, Linux RAID <linux-raid@vger.kernel.org>
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Ming Zhang wrote:

>>component partitions, e.g. /dev/sda7: 39MB/s
>>raid device /dev/md2:                 31MB/s
>>lvm device /dev/main/media:           53MB/s
>>
>>(oldish system - but note that lvm device is *much* faster)
>>    
>>
>
>this is so interesting to see! seems that some read ahead parameters
>have negative impact.
>  
>
I guess each raw device does some readahead, then the md0 does some
readahead and then the lvm does some readahead. Theoretically the md0
and lvm should overlap - but I guess that much of the raw device level
readahead is discarded.

David

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