> > so a 4 x 40GB drive raid-5 array would give either 120GB (no hot-spare) > or 80GB (1 hot-spare)
Yeap... thats why I said both RAID 10 and RAID 5 in this case would give 80G usable. > > > > The question becomes... which provides more performance and is more > > > reliable? > raid 10 is slightly more reliable in theory (but only if you're lucky). > in practice...who knows? probably about the same. Seems about the same... but RAID 5 will allow any disk to die the 2nd time because the hot spare was used (only during reconstruction will the array not tolerate a second failure), while with RAID 10 you have 25% chance that the 2nd disk dying is the one you cannot have die (the one in the same stripe, if i am not mistaken). > raid5 is faster than raid10, which should be obvious when you think > about it. raid0 (stripe) is fast, but raid1 (mirror) is very slow...it > is certainly much slower to write the same data to two drives than it is > to write to the data to one drive plus a parity calc & write. with > raid10, you end up with a striped (double-speed) mirror (half-speed), > for no net speed gain over a single drive. it doesn't get any faster if > you add more disks, either. > > raid5 on the other hand stripes data and parity over all disks, so the > more disks in the array the faster it gets. Okay, so performance wise RAID 5 will be faster than RAID 10. > i did some benchmarks last year with an 8 drive scsi hardware raid > system to determine what configuration would provide the best > performance. i tested different raid configurations, different > filesystems (xfs, reiserfs, ext2), and different usage patterns > (simulations of file-server, mail-server, database-server etc type > loads) > > like you, i expected raid10 to be the fastest because that's what most > of the info on the net says. nope. i was surprised to find that raid5 > was significantly faster than raid10. > > > FWIW, i don't think it's possible to generalise about raid performance > and be at all accurate. it depends very much on whether you have > hardware or software raid AND on whether your raid controller has a > large *non-volatile* write-cache. 3ware hardware IDE raid. Their performance benchmarks show them to have some of the highest RAID 5 performance, but they didn't compare RAID 10 performance with other brands so I don't know how they stack up against eachother. > without the non-volatile write-cache, raid5 is very slow. with it, it > is very fast. > I would assume in this case that the 3ware card would have at least comparable performance. 3ware boasts that it has very good RAID 5 read/write algorithms, but I won't really know till i actually use it ;-) -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]