A couple of years ago two disks on my old (now defunct) EX4 died without warning at about the same time. (The second drive failed while rebuilding the RAID 5 after replacing the failed drive.) So everything lost. Bummer.
I’d probably kept the old disks going past their expected lifetime, but was a bit grumpy that the EX4 didn’t give any kind of warning of impending death. I guess I was expecting too much. Live and learn. The fact that the EX4 was getting pretty flakey may have contributed to the problem, too.
I now have an EX4100 running RAID 5 + spare. I’m not sure the spare is that much better than a 4-disk RAID 5, though the automatic activation of the spare would be handy. (The EX4100 does that, right? The manual doesn’t say.)
But, to my question: I’d like to protect myself against this kind of double failure in the future, and wonder how other EX Series users deal with this. One option, of course, would be to have a couple of spare drives on the shelf ready to swap in as needed. (I have one already, probably should get another.)
I’m using the WD Red drives, by the way. Whether that’s the best idea is another question, but kind of the idea of RAID is you can use cheaper (less reliable) disks and deal with the consequences.
Another option would be to replace the oldest disk every L/4 time, where L is the expected life of a disk. Expected life would probably be more than the warrantee period, but maybe not a lot more. And I’m thinking that the newest disk should be the new spare.
I’d be interested to hear thoughts and experience on this.