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Date: Fri, 23 Nov 2007 10:11:59 +0300
From: Alexey Popov <lol@chistydom.ru>
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To: Kris Kennaway <kris@FreeBSD.org>
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Cc: freebsd-hackers@freebsd.org, Panagiotis Christias <christias@gmail.com>,
	freebsd-stable@freebsd.org
Subject: Re: amrd disk performance drop after running under high load
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Kris Kennaway wrote:

>>>> what is your RAID controller configuration (read ahead/cache/write
>>>> policy)? I have seen weird/bogus numbers (~100% busy) reported by
>>>> systat -v when read ahead was enabled on LSI/amr controllers.
>>> I tried to run with disabled Read-ahead, but it didn't help.
>> I just ran into this myself, and apparently it can be caused by 
>> "Patrol Reads" where the adapter periodically scans the disks to look 
>> for media errors.  You can turn this off using -stopPR with the megarc gg 
>> port.
> Oops, -disPR is the correct command to disable, -stopPR just halts a PR 
> event in progress.
Wow! Really disabling Patrol Reads solves the problem. Thank you!

I have many amrd's and all of them appear to have Patrol Reads enabled 
by default. But the problem happenes only on three of them. Is this a 
hardware problem?

With best regards,
Alexey Popov