On 09/13/2013 05:47 PM, Grant wrote: > > I had no idea. How awesome. So the entire array shows up as /dev/sda > when using a real hardware controller? Just enable an extra kernel > config option or two and it works? >
Yep. >> Yes. RAID10 both stripes and mirrors. So you can lose one, and it's >> definitely mirrored on another drive. Now you have three drives. If you >> lose another one, is it mirrored? Well, maybe, if you're lucky. There's >> a 2/3 chance that the second drive you lose will be one of the remaining >> mirror pair. >> >> Recommendation: add a hot spare to the system. > > Would the hot spare be in case I lose 2 drives at once? It's just to minimize the amount of time that you're running with a busted drive. The RAID controller will switch to the hot spare automatically without any human intervention, so you only have to keep your fingers crossed for e.g. 3 hours while the array rebuilds. This is as opposed to 3 hours + (however long it took the admin to notice that a drive has failed). > Isn't that extraordinarily unlikely? If the failures were random, yes, but they aren't -- they just seem that way. The drives that you use in a hardware RAID array should ideally be exactly the same size and have the same firmware. It's therefore not uncommon to wind up with a set of drives that all came off the same manufacturing line at around the same time. If there's a minor defect in a component, like say a solder joint that melts at too low of a temperature, then they're all much more likely to fail at around the same time as the first one. > Are modern SSDs reliable enough to negate the need for mirroring or do > they still crap out? I don't have any experience with SSDs, but a general principle: ignore what anyone says, mirror them anyway, and make lots of backups.
