> -----Original Message----- > From: Mark Hahn [mailto:[EMAIL PROTECTED] > Sent: Monday, November 26, 2007 8:45 PM > To: Ekechi Nwokah > Cc: Beowulf Mailing List > Subject: RE: [Beowulf] Software RAID? > > >> Of course there are a zillion things you didn't mention. How many > >> drives did you want to use? What kind? (SAS? SATA?) If > you want 16 > >> drives often you get hardware RAID hardware even if you > don't use it. > >> What config did you want? > >> Raid-0? 1? 5? 6? Filesystem? > > > > So let's say it's 16. But in theory it could be as high as > 192. Using > > 16 drives in a system is reasonable. for much larger > systems, I would go for more scalable building blocks > (network connected, 10GE or IB.) > > > multiple JBOD cards that present the drives individually > (as separate > > LUNs, for lack of a better term), and use software RAID to > do all the > > things that a 3ware/Areca, etc. card would do across the > total span of > > drives: > > > > RAID 0/1/5/6, etc., hotswap, SAS/SATA capability, etc. > > software raid on 192 drives in a single system sounds > somewhat dubious. > not impossible, by any means, but you'll wind up challenging > the fact that commodity systems don't scale that high. I'm > guessing you'll need to use a bunch of SAS channels for > daisy-chainability. >
Something like that ;-). > > Right now, all the hardware cards start to precipitously drop in > > performance under concurrent access, particularly read/write mixes. > > I would consider turning off queueing in the card, and > leaving all the request sorting to the kernel. any ideal how > many requests a card typically takes upon itself to schedule > (afaik, disks themselves only ever sort fairly small > numbers.) since you depend strongly on very effective > sorting of requests, I'd lean towards trying to get the host > to do all the sorting. > Agreed. In that case you could buy much cheaper JBOD cards without any queueing at all. That's the point. > > I just haven't seen something like that and I was not aware that md > > could acheive anything close to the performance of a hardware RAID > > card across a reasonable number of drives (12+), let alone > provide the > > feature set. > > 12 disks is enough for MD to need some help - tweaking the > stripe cache, for instance. > > can I ask what the actual application is? > Large scale data mining. > regards, mark hahn. > Ekechi _______________________________________________ Beowulf mailing list, [email protected] To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf
