Something to think about – we had a couple of models from the same batch die within a day of each other recently, and while that may be coincidence there may also have been something about that batch that made them die under certain usage conditions or at a certain age. Now, if they had been a mirrored pair the mirror would have been lost and we’d have had to go to a backup to restore the data. Fortunately we had spread that batch out across several arrays so the failures didn’t result in any downtime and the drives have been RMA’d as per usual.
If you’re buying several drives at once this is something to keep in mind – try to source them from different batches if possible or spread the drives out so that if they do all fail in a short space you won’t lose anything. We certainly don’t keep our backups on the same media as our main arrays just in case something catastrophic happens to a batch of disks.
A good rule of thumb for valuable data is 3, 2, 1: 3 copies, 2 types of media, 1 offsite. If your data is important – family photos, important documents, anything that would be hard to replace or irreplaceable – remember to back it up. Even a drive or thumbdrive at a family member or friend’s house could save you if your home or work gets burgled.