Thanks to all for the feedback. To summarize: RAID6 advantages over RAID10 - greater fault tolerance - greater space efficiency with >4 drives - apparently easier to recover disadvantages - additional CPU overhead, reduced performance I still like the simplicity and ease of recovery of RAID1 (my original scenario B), with the performance advantages a bonus. But I plan to play around a bit, both for the practice and if I have time to do some benchmarking. >> I hadn't considered RAID6, as my understanding has been that it's >> usually implemented by specialized "enterprise-level" hardware, as >> opposed to my "consumer level" stuff, and much larger sets of disks >> than what I'm working with. > > Well, somewhat larger. Unless one is just starting out and plans to grow a > great deal, a RAID6 array of 4 drives is fairly inefficient, although no > worse than RAID1. A RAID6 array of 6 drives is fairly reasonable, though. > Beyond 6 drives, I definitely recommend RAID6. A hot spare is a good idea, > too. As far as requiring "enterprise grade" hardware, that's not the case, > at all. Indeed, given the relative frailty of "consumer grade" hardware, > RAID6 is all that more attractive. Sequential hard drive failiures are not > at all uncommon, given the size of many modern volumes. > >> Thanks Mikael, yes simplicity is critical to "ease of recovery", >> especially given my noobness. Are you saying RAID6 is "simpler" than >> RAID10? Actually your reminder of KISS is nudging me to straight >> RAID1, maybe even drop the LVM. > > RAID6 allows for high reliability, allowing up to 2 random volume > failures without taking the array offline. RAID10 can suffer more volume > failures, but only specific volumes can fail. If it is the wrong pair of > volumes, the array is toast. RAID6 allows for easier expansion with minimal > management from the admin. For your purposes, you could employ RAID6 for > your data volumes and then create RAID1 arrays of the RAID6 volumes for > backup purposes. You'll need to buy several more drives though. >> Although performance isn't such a big issue for me, my (several >> generations old now) CPU will already be handling all the disk I/O >> discussed - plus the filer's going to be serving out a >> yet-to-be-determined number of iSCSI LUNs, so I'm willing to trade off >> space penalty for the performance and (even more important) the >> simplicity of RAID1 or RAID10. >> >> Regarding the possibility (IMO slim) of the primary drive failing >> during a straight-mirror rebuild, the first (smaller) RAID set is > > It's not that slim, at all. > >> My understanding is that putting RAID10 on a single >> pair of disks is A- in effect the same as RAID1 in the event one of >> the drives fails but B- that there might be a performance boost in >> normal operations from the striping feature? >> >> And yes that's another question - feedback from anyone welcome. . . > > Yes. But you may only loose 1.3 disks - if one disk fails, it's ok, but > the second disk falure must happen at the right spot. Which makes it an > unsafe choice. > >> Thanks Mikael, yes simplicity is critical to "ease of recovery", >> especially given my noobness. Are you saying RAID6 is "simpler" than >> RAID10? Actually your reminder of KISS is nudging me to straight >> RAID1, maybe even drop the LVM. > > From the user-side and the ease of recovery-side RAID6 is simpler to handle. > -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
