Date: Tue, 4 Jan 2000 13:29:07 -0500 (EST) From: Jim Doherty <doherty@ans.net> To: Matthew Jacob <mjacob@feral.com> Cc: Mitch Collinsworth <mkc@Graphics.Cornell.EDU>, hardware@FreeBSD.ORG Subject: Re: differences between SCSI and EIDE [was: wanna buy an EIDE harddisk ... 5400 or 7200 for home use (noise)] Message-ID: <Pine.GSO.4.05.10001041317570.5846-100000@sandcastle.ny.ans.net> In-Reply-To: <Pine.BSF.4.10.10001040917470.4553-100000@beppo.feral.com>
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On Tue, 4 Jan 2000, Matthew Jacob wrote: > > On the other hand, the newer bigger drives are getting able to basically > consume most available bus bandwidth. If the numbers I've seen recently > for drives being able to do ~24MB/s off the platter are indicative of There is a big difference between raw bandwidth and actual usage patterns. Accessing a lot of small files drives a lot of overhead and you are lucky to drive more than a couple hundred KB. I once copied a large news spool off of a 9 gig drive and had the copy operation take over 8 hours on an AIX system. By unmounting the filesystem and performing a copy of the logical volume it took under an hour. The filesystem overhead in opening/closing/seeking files has a big impact on being able to drive i/o. For everything but writing/reading very large files the SCSI bus is not going to be the limit. My guess is that the overhead in the standard i/o libraries might even be able to get in the way, but I have not measured it. Jim Doherty > things to come, then another reason for using SCSI (shared interleaved > usage of an I/O bus) is going away because the limit is moving from the > primary PCI bus to the seconday I/O bus, and if you can fit 4 ~20MB/s or > better drives into a system (consuming most of the usable PCI bus > bandwidth while you're at it) at a fraction of the cost for an Ultra2 LVD > bus (which maxes out at 80MB/s), then indeed why bother with SCSI? > > -matt > > To Unsubscribe: send mail to majordomo@FreeBSD.org > with "unsubscribe freebsd-hardware" in the body of the message > To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hardware" in the body of the message
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