From owner-freebsd-hardware Tue Jan 4 10:29:20 2000 Delivered-To: freebsd-hardware@freebsd.org Received: from sandcastle.ny.ans.net (sandcastle.ny.ans.net [147.225.51.62]) by hub.freebsd.org (Postfix) with ESMTP id 2FF3E14E27 for ; Tue, 4 Jan 2000 10:29:17 -0800 (PST) (envelope-from doherty@ans.net) Received: from localhost (doherty@localhost) by sandcastle.ny.ans.net (8.8.7/8.8.7) with ESMTP id NAA06300; Tue, 4 Jan 2000 13:29:07 -0500 (EST) X-Authentication-Warning: sandcastle.ny.ans.net: doherty owned process doing -bs Date: Tue, 4 Jan 2000 13:29:07 -0500 (EST) From: Jim Doherty X-Sender: doherty@sandcastle.ny.ans.net To: Matthew Jacob Cc: Mitch Collinsworth , hardware@FreeBSD.ORG Subject: Re: differences between SCSI and EIDE [was: wanna buy an EIDE harddisk ... 5400 or 7200 for home use (noise)] In-Reply-To: Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-freebsd-hardware@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.org 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