Date: Fri, 23 Nov 2007 11:54:00 +0100 From: Kris Kennaway <kris@FreeBSD.org> To: Alexey Popov <lol@chistydom.ru> 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 Message-ID: <4746B148.6000209@FreeBSD.org> In-Reply-To: <47467D3F.7020002@chistydom.ru> References: <47137D36.1020305@chistydom.ru> <47149E6E.9000500@chistydom.ru> <4715035D.2090802@FreeBSD.org> <4715C297.1020905@chistydom.ru> <4715C5D7.7060806@FreeBSD.org> <471EE4D9.5080307@chistydom.ru> <4723BF87.20302@FreeBSD.org> <47344E47.9050908@chistydom.ru> <47349A17.3080806@FreeBSD.org> <47373B43.9060406@chistydom.ru> <e4b0ecef0711111531k449f78fbnf7f3241b768498ad@mail.gmail.com> <4739557A.6090209@chistydom.ru> <4741EE9E.9050406@FreeBSD.org> <474492B0.1010108@FreeBSD.org> <47467D3F.7020002@chistydom.ru>
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Alexey Popov wrote: > 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? I am not sure, maybe for some reason the patrol reads are not interfering with other disk I/O so much (e.g. the hardware prioritises them differently or something). Anyway, glad to hear it was resolved. Kris
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