If you are some insane masochistic systems admin who loves rebuilding RAID 5 arrays from the ground up every time HDD sizes increase, pay attention; by 2009 you could have a 7 disk RAID5 array built of 2TB drives.  If you connect that 12TB to plain old SATA connections on a discount RAID card and never back-up the drives to any other medium, when one disk on the RAID fails there is a very good chance that a disk read error will travel up the chain of drives and take the whole RAID out.

As most moderately sane systems admins (loosely speaking, of course) do not use huge disks in RAID arrays, or use RAID6, 50 or other formats if the disks do have to be large, they don’t have to worry about SATA’s specified unrecoverable read error rate (URE) of 10^14, aka 12TB.  Said admins also tend to have off-site backups, burned copies of critical files and perhaps even tape drives. 

If you are the first type, get help.  If you are the second type, then smirk along with the folks of Slashdot at this new and improved version of old FUD.

“Lally Singh recommends a ZDNet piece predicting the imminent demise of RAID 5, noting that increasing storage and non-decreasing probability of disk failure will collide in a year or so. This reader adds, “Apparently, RAID 6 isn’t far behind. I’ll keep the ZFS plug short. Go ZFS. There, that was it.”

“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 – you thought! – data is gone. Oh, you didn’t back it up to tape? Bummer!”

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