Date: Sat, 23 Nov 2002 16:47:24 -0800 From: Paul Saab <ps@yahoo-inc.com> To: Pete French <pfrench@firstcallgroup.co.uk> Cc: stable@FreeBSD.ORG Subject: Re: RAID performance problems Message-ID: <20021124004724.GA24189@yahoo-inc.com> In-Reply-To: <E18FfTI-0004KM-00@mailhost.firstcallgroup.co.uk> References: <E18FfTI-0004KM-00@mailhost.firstcallgroup.co.uk>
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Are you sure the Battery module is installed? If it isn't, then the read/write cache would not be enabled. Pete French (pfrench@firstcallgroup.co.uk) wrote: > I wonder if anyone can shed any light on the following, as I am > starting to come to the conclusion that its possibly some BSD driver > issue. > > I have been testing the performance of the various drives on my system > using bonnie, just out of curiosity. The system has 3 different drives on > it: > > 1) a 15k RPM drive attached directly to an Adaptec SCSI controller > 2) a RAID-1 mirrored pair of 10k RPS drives > 3) a RAID-5 set of 5 7200 RPM drives > > All SCSI buses are 40MB/sec. Both the RAID drives are being run from the > same Compaq 4200 RAID controller. Both the RAID controller and the Adaptec > SCSI card are on the same PCI bus. > > So, what I expected was that the driect drive would be fastest, followed by > the RAID-1, then the RAID-5 (at least as far as write performance goes) > > The actual results are that both the RAID drives have identical performance! > The direct drive is 4 times faster than these. > > This was a bit of a shock to me. Especially ater all the effort of utting > in thr 10k RPM drives to try and speed that disc up. The obvious conclusion > is that somewhere there is some component common to both RAID drives which is > limiting the performance. > > The bottleneck cannot be the PCI bus to the card as the direct drive is > shifting 4 times the data on the same bus. It also cannot be the SCSI > bus to the drives by my reasoning - even assuming that the controller > aggregates the writes so that RAID-5 and RAID-1 are taking the same bandwidth > on the bus (which is necessary if they are to perform the same with the bus > being the bottleneck right?) then the bus is operating 4x slower than the > direct bus. The Compaq card supports 40MB/s bus speeds according to > the documentation - plus the bus is terminated correctly as plugging the array > into the SCSI card shows all the drives up as 40MB/s > > So I'm left with one of two conclusions > > a) This is a limitation in the processing power of the RAID card. This seems > very unlikely - the work needed to be done by the controller for RAID-1 > is far less than that which needs to be done for RAID-5 (it would take a > complete muppet to design a controller where this wasnt the case wouldnt > it ?) and this is one of Compaq's meatier controllers afer all. > > b) This is some strange limitation in the speed at which FreeBSD's device > driver for Compaq controllers can talk to the actual device. > > Its the fact that I have arrived at conclusion b) as a possibility that makes > me ask on here. Does anyone have any comments or thoughts on this ? I know > there are people around who can argue at great length about RAID performance > after all :-) > > -pcf. [puzzled] > > To Unsubscribe: send mail to majordomo@FreeBSD.org > with "unsubscribe freebsd-stable" in the body of the message > To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-stable" in the body of the message
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