The advantage of the "safe" RAID levels (ie., not JBOD and STRIPE, but MIRROR and the various PARITY types) is that you can indeed keep on working, you don't lose data, and you can plug in a healthy drive and repair the array (very
nice feature if your hardware is hotplug-able).
Problem with RAID-5 rebuilding is that it's more intensive than the simple copy done with RAID-MIRROR. Also, because RAID-5 can still only tolerate one failing disk, the more disks you add to the array, the higher risk of failure you have.
If you buy two identical harddrives from the same batch, statistically the drives will fail within a relatively short timeframe (couple of months or something like that) - and in case you don't have a proper intake fan to cool the drives, you run a much
higher risk of more than one drive saying bye-bye.
So if I schedule backup daily of all important files & folders, there really no sense in even running RAID-MIRROR?
Yes, because drives always fail one hour before you do your backup
dont really understand the atttraction of fast drives if they need more fans/get very hot but then I've never used one.
My raptor don't seem to get much hotter than other drives I've used, even though it's 10,000rpm. But I'll never
again build a system that doesn't have a 80mm or 120mm intake fan in front of harddrives, it's plain folly. Just buy a quality fan and you won't notice it's there. The advantage of 80mm and 120mm fans are that they're pretty quiet, and the noise they make is "deep", compared to the "whiny" (and highly
annoying!) fans on graphics cards, for instance.
(I mean I'd prefer quieter machine to shaving seconds...)
am considering something like a hotswap bay in the future (I only have the option to add one more drive i think..)
Be careful which one you get - you'll want one that keeps the drive cool. The fans in the (non-enterprise class
) hotswap bays I've seen have been very tiny and high-pitched and annoying.