On Aug 31, 2009, at 11:13 AM, Les Mikesell <lesmikesell at gmail.com> wrote: > Chan Chung Hang Christopher wrote: >> >> Oh sorry, I have never argued about eight drive systems years ago >> (didn't have them then, too poor) and there is no argument about >> raid1+0 >> being the way to do it beyond four drives. It is too obvious that >> stripping three drives and then mirroring them is more risky than >> making >> three mirrors and then stripping them. Any argument then about >> whether >> one should do raid0+1 were really limited to those who had four drive >> systems and never thought beyond four drives. >> >> So it is really moot unless one ignores the obvious or fails to >> think. >> >>> "Another difference between the two RAID configurations is >>> performance >>> when the system is in a degraded state, i.e. after it has lost one >>> or >>> more drives but has not lost the right combination of drives to >>> completely fail." >>> >>> RAID 1+0 is still more secure." >>> >> Hear, hear. Man, I should leave the 90s back there. > > But note that drive capacity has gone up too, often eliminating the > need > for many-disk arrays. For example, you can go up to 2TB on a single > drive, so a simple RAID1 mirror may be all you need, and if you can > arrange the mount points to match the use pattern you may get better > performance out of several separate raid1 partitions where the heads > can > seek independently instead of essentially tying them all together in a > single array. A many-disk array may do better on artificial benchmarks > accessing one big file, but that's not what most computers actually > do - > and raid1 has the advantages of not slowing down when a member fails > and > you can recover the data from any single drive. Ah the larger capacity is double sided as it also increases the chance of a double failure in a single parity RAID as the resilver time is also substantially increased, so if doing parity on large drives you should really go for RAID6, which unfortunately means you really need 5 drives over 3 to get the same economy as a RAID5. -Ross