Increasing storage and probability of hard disk failure will crash into eachother in a year or so. Apparently, RAID 6 isn't far behind. Disk drive capacities double every 18-24 months. We have 1 TB drives now, and in 2009 we'll have 2 TB drives. With a 7-drive RAID 5 disk failure, you'll have 6 remaining 2 TB drives. As the RAID controller is busily reading through those 6 disks to reconstruct the data from the failed drive, it is almost certain it will see an unrecoverable read error. So the read fails ... The message 'we can't read this RAID volume' travels up the chain of command until an error message is presented on the screen. 12 TB of your carefully protected data is gone. Oh, you didn't back it up to tape? Bummer!