RE: Informix and RAID

Your comparing apples to oranges. If I took your Shark 800 and mirrored each of its drives to its counterpart on another Shark 800 and striped those 8 drive pairs together using a third party VM like Veritas I'd have 8 pairs to your 7 and twice as much bandwidth to the drives. I think, no I'm positive I'd blow the doors off your 7 drive RAID5 array in read performance alone. Also did you test write performance? I suspect the 4 pair RAID10 STILL beats the 7 drive RAID5 by a bit or is right on its tail with nearly half as many spindles. You're fooling yourself on the performance. Beyond that if, as Obnoxio points out, you lose a second drive before rebuild completes you're cooked. My RAID10, even your 4 pair array, can survive losing half of its drives (as long as no two are in the same pair which is 70% less likely than the RAID5 losing ANY other drive) and still recover all of my data. Beyond that, during recovery the RAID5 array's performance will tank by 80% while performance of the 4 pair RAID10 array will degrade by less than 20% and complete recovery 25% faster. Shorter recovery means we're even less likely to lose another drive before recovery completes in the RAID10 than in RAID5. Did you READ my posting on the BAARF site? This is all detailed there and I CLEARLY state that performance is the smallest part of my objections to RAID5. Safety and performance during recovery are first and second. Art S. Kagel ----- Original Message ----- From: Willem Roos <wroos@shoprite.co.za> At: 12/15 1:52 > > We use IBM Shark (the 800 model) which can do both RAID5 & 10. For very > sequential I/O RAID5 is even faster than RAID10 (as quoted by IBM). > > This, i think, is because of the physical configuration of the disks in > groups. The maximum number of disks participating in a RAID > configuration is 8. Hence RAID10 gives you a stripe of 4 disks, and > RAID5 gives you a stripe of 7 disks (3 and 6 resp. when the hot spare is > carried in the group). > > So there's a case where RAID5 gets close to, and some times even beats, > RAID10 :-! > > > -----Original Message----- > > From: owner-informix-list@iiug.org > > [mailto:owner-informix-list@iiug.org] On Behalf Of Art S. Kagel > > Sent: 14 December 2004 17:25 > > To: informix-list@iiug.org > > Subject: Re: Informix and RAID > > > > Db Solution wrote: > > > I'm sorry but I think you are wrong. > > > > > > I repeat for small/medium installations RAID 5 is a OK > > solution. Back > > > in the day I personally used it and was satisfied with it. A lot of > > > customers are still using it are happy with it. > > > > > Lots of folk use LSD too, doesn't make it something I'd > > recommend or use > > myself. In fact it reminds my alot of RAID5. When it's good > > it's good. > > But, when you crash it can be fatal or you could lose your mind! > > > > Check out the BAARF site. There are lots of brief "I didn't > > believe until I > > lost a second RAID5 disks before the first one rebuit. No > > more RAID5 for > > me." testimonials on the membership list page. Also, let me > > as everyone > > whose been bitten by RAID5: Please post a short war story to > > enlighten Db. > > You can read mine in my RAID5 Rant on BAARF. > > > > Art S. Kagel > > > > Disclaimer > http://www.shoprite.co.za/disclaimer.html sending to informix-list