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From: Pete French <petefrench@ticketswitch.com>
Date: Thu, 09 Nov 2006 12:52:23 +0000
Cc: freebsd-stable@freebsd.org
Subject: Re: Dissapointing performance of ciss RAID 0+1 ?
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> It would be interesting for you to track iostat (i.e. run "iostat 1") 
> with and without modified vfs.read_max and see if there's a difference.

On the file: KB/t is about 127.5 with both sizes. Rate is 39 on with
the read_max set to 8, but 115 with read_max set to 64.

On the raw device: KB/t is always 128. rate is 41 with the size set to 8
but rises to 57 with the size set to 64! How can the vfs parameters affect
access to the raw device ?

> In a similar experiment, you could watch gstat (also before and after) 
> and see if it reports the difference.

On the file: read_max=8 gives 75% busy, 42 meg/sec. 64 gives 99.7% and 120
On the device: both sizes give the same results - 98% busy, 59 meg/second

I am not sure this is helping my understanding! :-)

-pete.