Originally Posted by guyladouche
Because raid 1 is designed for functional redundancy, not data backup or an actual method of data redundancy. If one drive physically fails (like, hardware failure) while your computer is actually running, the computer will continue to function--this would be for something that's time-critical that can't suffer from downtime. But it doesn't do anything to back up data whatsoever. Raid1 mirrors but it doesn't do anything about data integrity. It's a "dumb" method (for lack of a better term) that goes "okay, this bit is on this sector of that hard drive, I'm making a copy of it." There's no way for raid 1 to know if that bit of data is what the user intends it to be (i.e., it could be corrupted).
For example, you could encounter a situation where we did--you get some issue that affects your primary disk--in my situation we believed it to be a power surge--which causes massive data corruption on the primary hard drive. All of that corrupted data simply got mirrored to the second disk (because that's what raid 1 does--it mirrors). And because no one was conscientious about external backup of their data, a lot of data was lost and we had two corrupted disks instead of just one.
Note, this may not be a common occurrence. But I would argue that we keep backups just because of the fact that uncommon occurrences are possible. Never again have I bothered with the idea of a raid 1 disk.
If you're looking for an actual backup method, I've found that nothing beats an external hard drive that you use for periodic manual backups, and disconnect from your system.
I totally agree with this even though i have 2 x RAID1 arrays, why for mission-critcal services. I do weekly back ups of these arrays to singular external HDDs. Edited by stubass - 10/27/11 at 1:39pm