Date: Sun, 02 Jul 2000 18:51:09 -0700 From: Kent Stewart <kstewart@3-cities.com> To: David Gilbert <dgilbert@velocet.ca> Cc: freebsd-stable@freebsd.org Subject: Re: Dump takes ages on SCSI. (several times faster on IDE) Message-ID: <395FF18D.6B47A620@3-cities.com> References: <14687.42282.873585.2561@trooper.velocet.net> <395FB9EA.E3115939@3-cities.com> <14687.57741.726207.302060@trooper.velocet.net>
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David Gilbert wrote: > > >>>>> "Kent" == Kent Stewart <kstewart@3-cities.com> writes: > > >> I then noticed that the IDE would crashdump somewhere around 10 > >> times faster than the SCSI disk. > >> > >> Why? Can the SCSI speed be improved? > > Kent> It depends on what 2940 and what IDE drive you are talking > Kent> about. I have a Maxtor UDMA66 that is 20MB/s faster in some > > I don't think this explains it at all. It would appear that the SCSI > driver is running in some "extra safe" mode, or something. It has > 512M to write sequentually to a partition... and the counting on the > screen, we're looking at 2 to 3 seconds-per-megabyte (on a drive that > delivers write performance of about 10M/s in normal operation). > > Maybe what I should have said that the ratio of regular operation to > dump performance of the ide driver is about 1:1 while it's 10:1 for > the SCSI driver... why is this? I don't have any idea up front. One thing comes to mind and that is does your Quantum come up with "tagged queuing enabled". My IBM has that disabled or more precisely never enabled, which makes it slower and safer. My dmesg shows the drive as da0: <IBM DCAS-34330W S65A> Fixed Direct Access SCSI-2 device da0: 40.000MB/s transfers (20.000MHz, offset 8, 16bit) da0: 4134MB (8467200 512 byte sectors: 255H 63S/T 527C) My DCAS drive has tagged queuing disabled at the driver level. You can find out by looking for your drive in /usr/src/sys/cam/cam_xpt.c Beyond that I don't have any idea. People have always told me scsi was faster but I think that is like everything else in computing. There is a time and a place where it may not be. Some of the IBM lvd's were rated at 20MB/s continuous. The rate between the card and the drive was claimed to be much faster. Once you fill the cache you are down to the continuous rate. You will probably have to visit Quantum to find out what your drive is rated at. All of the rates on the Scsi 160's are higher yet. Kent -- Kent Stewart Richland, WA mailto:kstewart@3-cities.com http://www.3-cities.com/~kstewart/index.html FreeBSD News http://daily.daemonnews.org/ SETI(Search for Extraterrestrial Intelligence) @ HOME http://setiathome.ssl.berkeley.edu/ Hunting Archibald Stewart, b 1802 in Ballymena, Antrim Co., NIR http://www.3-cities.com/~kstewart/genealogy/archibald_stewart.html To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-stable" in the body of the message
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