Date: Wed, 23 Jul 1997 16:17:16 -0400 From: "Gary Palmer" <gpalmer@FreeBSD.ORG> To: Simon Shapiro <Shimon@i-Connect.Net> Cc: freebsd-scsi@FreeBSD.ORG Subject: Re: New DPT Driver Message-ID: <6771.869689036@orion.webspan.net> In-Reply-To: Your message of "Wed, 23 Jul 1997 00:29:43 PDT." <XFMail.970723002943.Shimon@i-Connect.Net>
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Simon Shapiro wrote in message ID <XFMail.970723002943.Shimon@i-Connect.Net>: > RAID Corner: > > * Use RAID-(!0) only if data loss is very upsetting. > * Use RAID-5 only if storage space is at premium. > * Remember that RAID array MTBF is (worst drive MTBF) / (number of drives) > A redundant array simply provides a way to recover from this formula. > > Many people use DPT cotrollers for News Servers, and use RAID-5 > configuration. When i grew up, losing the news data was upsetting but not > a disaster. Performance in this convoluted database is important. > If you agree with this statement, use RAID-0. If this is wrong, use RAID-5. > If you need the best performance, in a redundant array, use RAID-1. > An interesting combination is to create several RAID-1 arrays, and then > have CCD across them in a RAID-0 (striping) arrnagement. > > REQUEST: > > Please try and build several different RAID configurations and try to see > which is the best solution for news servers. I have enough questions on > this matter i think I will start selling tickets :-) The most common scenario I've heard of for large news installations, where drive numbers are not a problem and you can get as many drives as you ask for, they use RAID0+1, i.e. take 2 identical stripes and mirror then. Of course, the RAID format you choose is only one part of a very large equation ... some people swear by 1gig drives, and lots of them, to get the needed performance. Others swear by 4gig drives. Then you get into the whole narrow/wide/ultrawide argument, and how many drives are optimal to put on a single scsi chain, how many chains you need, etc. Then there is the sticky issue of what stripe size to use. You, in the past, have recomended small stripe sizes for use in the DPT controller. I am not sure if that is because of hardware/software limitations or an over-generalisation. The growing consensus is that larger stripe sizes are better for news (sizes on the order of 32MB, yes, thats 32 megabytes) are non unusal. Can DPT support that? Gary -- Gary Palmer FreeBSD Core Team Member FreeBSD: Turning PC's into workstations. See http://www.FreeBSD.ORG/ for info
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