Date: Tue, 14 Jun 2005 21:22:01 +1000 (EST) From: Bruce Evans <bde@zeta.org.au> To: Glenn Dawson <glenn@antimatter.net> Cc: freebsd-scsi@freebsd.org Subject: Re: Accessing SCSI-Devices >2TB Message-ID: <20050614211046.G38218@delplex.bde.org> In-Reply-To: <6.1.0.6.2.20050613235825.09e52810@cobalt.antimatter.net> References: <20050608171130.GA64736@over-yonder.net> <1118252322.7479.28.camel@zappa.Chelsea-Ct.Org> <20050609113616.I41471@p-i-n.com> <20050609130511.GA732@uk.tiscali.com> <20050610162814.A25098@p-i-n.com> <20050610150718.GA7005@nargothrond.kdm.org> <20050612002508.B25098@p-i-n.com> <20050612035440.GA21262@nargothrond.kdm.org> <CD88CCB1DE9CF5C39930AE6E@aslan.scsiguy.com> <20050613121915.C25098@p-i-n.com> <20050614015958.GA33865@nargothrond.kdm.org> <42AE5ED7.8070309@samsco.org> <6.1.0.6.2.20050613235825.09e52810@cobalt.antimatter.net>
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On Tue, 14 Jun 2005, Glenn Dawson wrote: > This is a little OT for this thread, but I'm currently trying to solve a > problem which might be related to the aac driver, so I'll toss this out there > and see if anyone has any ideas for me. It seems to be very OT :-). > It trying to make the transition from 4.x to 5.x I've noticed that > performance of the md(4) (in 5.x) driver seems to be much worse than the > vn(4) driver under 4.x. > > Here's the scenario: > > A pair of mirrored disks on an adaptec 2120S using the aac(4) driver is being > used to house files that are the backing store for a number of virtual disks. > Each file is typically about 4GB. > > Under 4.11 using the vn(4) driver I see throughput of about 17MB/sec when > writing to one of the virtual disks (using dd). > > Under 5.4 using the md(4) driver I only see throughput of about 7MB/sec when > writing to the virtual disk. This seems to be from sync writes now being the default for md. Try using "mdconfig -o async ...". I will reply with more details to your message in freebsd-performnance. Bruce
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