Recently there has been posted a couple of quite interesting papers about storage, disk reliability and more. This article is a good summary and Netapp have responded with a long and interesting reply. As a person that have just invested in a RAID 5 NAS (Network Attached Storage) system, it is a bit worrying to read things like this:
. . . a key application of the exponential assumption is in estimating the time until data loss in a RAID system. This time depends on the probability of a second disk failure during reconstruction, a process which typically lasts on the order of a few hours. The . . . exponential distribution greatly underestimates the probability of a second failure . . . . the probability of seeing two drives in the cluster fail within one hour is four times larger under the real data . . . .
Netapp comments on that with this:
...protecting online data only via RAID 5 today verges on professional malpractice.
Quite disturbing...I guess we can only hope that something better will soon become widely available, not only for the enterprise, but also for the growing marked of consumer NAS products.