Comment: Only caveat: Use RAID6 not RAID5 (Score 1) 355
The argument for using RAID6 (2 parity drives instead of 1) is that with the larger drives (1TB and up) if you have a hardware failure in one of your large drives (probably all from the same lot, possibly with sequential serial numbers and all with an effectively identical environmental history), your odds of having a second failure during a very long rebuild are not negligible. Your example of effectively 1% per hour on the rebuild should scare the crap out of many people - particularly if they've also been sloppy about backing up that 12+TB of data which is pretty likely.
Basically, if you have a pretty full RAID5, replace it with a RAID6 of significantly larger drives - get the extra redundancy, get some growth space, and take that RAID5 somewhere else - preferably preserved as a snapshot or used as a seed for offsite backup if you don't already have a good backup routine.
Basically, if you have a pretty full RAID5, replace it with a RAID6 of significantly larger drives - get the extra redundancy, get some growth space, and take that RAID5 somewhere else - preferably preserved as a snapshot or used as a seed for offsite backup if you don't already have a good backup routine.