Date: 09 Aug 1997 00:54:13 +0200 From: Peter Mutsaers <plm@xs4all.nl> To: freebsd-current@freebsd.org Subject: Re: IDE vs SCSI was: flags 80ff works (like anybody doubted it) Message-ID: <877mdw2smi.fsf@plm.xs4all.nl> In-Reply-To: "John S. Dyson"'s message of Thu, 7 Aug 1997 23:27:18 -0500 (EST) References: <87k9hw723z.fsf@totally-fudged-out-message-id>
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>> On Thu, 7 Aug 1997 23:27:18 -0500 (EST), "John S. Dyson" >> <toor@dyson.iquest.net> said: JSD> This is the result of my "slow" recent, but not the latest, greatest JSD> IDE drive (WD 4GB drive.): JSD> Command overhead is 88 usec (time_4096 = 348, time_8192 = 607) JSD> transfer speed is 1.57828e+07 bytes/sec JSD> dd if=/dev/rwd1 of=/dev/null count=1600 bs=64k JSD> 1600+0 records in JSD> 1600+0 records out JSD> 104857600 bytes transferred in 10.881267 secs (9636525 bytes/sec) JSD> This is the result of my Hawk, SCSI drive, with an NCR 815 interface: JSD> Command overhead is 845 usec (time_4096 = 2071, time_8192 = 3297) JSD> transfer speed is 3.34201e+06 bytes/sec JSD> dd if=/dev/rsd0 of=/dev/null count=1600 bs=64k JSD> 1600+0 records in JSD> 1600+0 records out JSD> 104857600 bytes transferred in 27.336979 secs (3835742 bytes/sec) Hmm, my NCR815 does: ~> dd if=/dev/rsd2 of=/dev/null count=1600 bs=64k 1600+0 records in 1600+0 records out 104857600 bytes transferred in 15.215823 secs (6891352 bytes/sec) This is a seagate ST15150N. But for Wide and/or Ultra SCSI you can expect better values. More interesting is: ~> dd if=/dev/rsd0 of=/dev/null count=1600 bs=64k&;dd if=/dev/rsd0 of=/dev/null count=1600 bs=64k& [2] 16410 [3] 16411 i.e. start two of them at the same time. I get as result: 104857600 bytes transferred in 41.430049 secs (2530955 bytes/sec) and 104857600 bytes transferred in 41.437855 secs (2530478 bytes/sec) So still >5MB/s What does IDE do in this case? Another variant: ~> dd if=/dev/rsd0 of=/dev/null count=1600 bs=64k&; sleep 2; dd if=/dev/rsd0 of=/dev/null count=1600 bs=64k& [2] 16415 [3] 16417 i.e. two of them, but with 2 seconds wait in between to make sure that the two readers do not read blocks that are very close. Results are much, much lower now: 104857600 bytes transferred in 113.343774 secs (925129 bytes/sec) and 104857600 bytes transferred in 113.277994 secs (925666 bytes/sec) Less than 1 MB/s total throughput remains! Quite dissapointing. I wonder how IDE behaves in this case. Anyway, apart from performance, I mainly use SCSI because I have 3 disks, a CD-ROM and a tapestreamer all on 1 cable, all with good drivers and very reliable. -- /\_/\ ( o.o ) Peter Mutsaers | Abcoude (Utrecht), | Trust me, I know ) ^ ( plm@xs4all.nl | the Netherlands | what I'm doing.
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