Date: Mon, 21 Sep 1998 16:20:09 -0700 From: David Greenman <dg@root.com> To: spork <spork@super-g.com> Cc: Omar Thameen <omar@clifford.inch.com>, hardware@FreeBSD.ORG Subject: Re: SCSI card used at cdrom.com? Message-ID: <199809212320.QAA18709@implode.root.com> In-Reply-To: Your message of "Mon, 21 Sep 1998 18:27:42 EDT." <Pine.BSF.4.00.9809211822520.2991-100000@super-g.inch.com>
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>I'd like to throw my question out again, with a bit more of a general >slant to it: > >Does everyone find the adaptec 2940xxx to be reliable and stable? Yes, absolutely. >And to David, may I ask a bit about how you came to choose the Mylex raid >controller over the CMD? We have pretty much settled on the CMD after >many recommendations, but I'd like to hear some of your reasons for going >with the Mylex... I had, too, chosen the CMD until I found out that it only supports 32 tagged commands total. Maximally configured (45 drives), this means that not only would the CMD controller be unable to queue more than one command per disk, but in fact 1/3 of the disk drives would be completely idle at any given time. I was originally alerted that this may be a problem by looking at the product literature which indicated that 64 tagged commands was the limit. I called CMD and talked to a guy there about it and he told me that in more recent revs the tagged command limit had been further decreased to 32 commands due to a memory shortage on the controller. This problem forced me to look elsewhere, and the Mylex was what I found. The Mylex could be better in the transactions per second area (which I've benchmarked to be 1138/sec), but it's high enough for our purposes. I also looked at the Adaptec, but it doesn't support enough cache RAM - I considered 256MB a minimum, and I believe the Adaptec supported only 32MB. I think the Adaptec had only 3 SCSI busses, and I was looking for a minimum of 5. -DG David Greenman Co-founder/Principal Architect, The FreeBSD Project To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hardware" in the body of the message
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