Date: Tue, 27 Mar 2001 12:06:20 -0800 From: Michael VanLoon <MichaelV@EDIFECS.COM> To: "'Andrew C. Hornback'" <hornback@wireco.net>, Joseph Gleason <clash@fireduck.com> Cc: FreeBSD Hardware <hardware@FreeBSD.ORG>, 'Ed Henderson' <Ed.Henderson@Certainty.net>, 'Mike Smith' <msmith@freebsd.org> Subject: RE: Server MB suggestions? Message-ID: <F37F6A0194D1EF4BA8D0EF3B542BE3E00F155D@ecx1.edifecs.com>
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> From: Andrew C. Hornback [mailto:hornback@wireco.net] > Sent: Tuesday, March 27, 2001 7:46 AM > > > -----Original Message----- > > From: owner-freebsd-hardware@FreeBSD.ORG > > [mailto:owner-freebsd-hardware@FreeBSD.ORG]On Behalf Of > Joseph Gleason > > Sent: Monday, March 26, 2001 7:10 PM > > To: Michael VanLoon; Ed Henderson; freebsd-hardware@FreeBSD.ORG > > Subject: Re: Server MB suggestions? > > > > Some of the 3ware products will take 8 drives. If you > stock it with 75gb > > drives that is 600gb. If you need more than that, I guess > this probably > > isn't the solution for you. > > > > The 3ware cards will do the RAID with IDE. I don't want to > start a holy > > war, but I really see no need for SCSI if you follow a few basic > > rules with > > your IDE drives. > > > > 1) Get good drives (IBM) > > Agreed. They make the best drives, hands down. Also agreed. > > 3) Keep it at one drive per chain. I am no hardware > expert, but it is my > > understanding that there are major performance hits if you > have two drives > > on a single chain. > > That last assertion depends on the controller, the > drives and the RAID > schema that you are using (i.e. SCSI). > > Hang 4 Ultra160 drives off of a UW controller, and > you're going to see > performance dips. Hang 4 UW drives off of an Ultra160 > controller, and you > should (if configured properly) see a performance increase. Not sure what you were trying to say here... :-) > You have to remember that for RAID 1 (or other > mirroring setups) for every > read request, you're hardware is actually doing two (or > more). But, you can > regain some of that performance by going to a striping schema > which allows > the hardware to read across more than one physical drive, > utilizing higher > output. I think you have that backwards. Reading mirrors, with a good controller, increases performance, not decreases. A good hardware RAID controller will interleave read requests from mirrored drives so you can approach double the read throughput of a single drive. And writes should be the same speed (roughly) writing to two drives as one, since they're simultaneous. Of course in reality, bus bandwidth comes into play, and is one of the reasons lots of installations install each pair of mirrored drives on separate SCSI busses. Here are the benefits of SCSI hardware RAID over IDE RAID: - More performance with lots of drives, both because you can have more drives on more busses, and because the RAID is actually happening on the controller (many IDE "hardware" RAID controllers do only the basic work needed, and much is still done in the BIOS or the OS). - More extensible. With a 3-bus SCSI controller you can hang up to 45 devices off it. It's pretty easy to max out an IDE RAID controller and have nowhere to go. - More easily extensible. A good hardware RAID controller will allow you to do dynamic expansion of the volume. I.e., throw a couple more drives on, tell the controller to expand it, it does so in the background, rearranging the pieces of the array for optimum performance, and viola, you have a larger virtual drive. Then you just need to use the OS to either expand the filesystem/partition (i.e. growfs), or add a new one. - Reliability. SCSI drives are simply more reliable. IDE drives are made with cost as the primary requirement. They fail more often. Please don't flame me on this. Yes, SCSI drives fail, and yes lots of IDE drives last a long time, but over a large sample, it's pretty much a fact that IDE drives have more failures than SCSI drives. On the other hand, yes modern IDE drives are fairly well built, pretty fast, and cheap cheap cheap. Balance as your needs, comfort level and budget can accommodate. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hardware" in the body of the message
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