I've thought this for a while. Ideally, you want to have drives of different ages, so they're at different pts of the 'bathtub curve'.
If you're mirroring, you should only ever mirror a "fresh, unproven" disk with an "old stalwart" disk. Doing that also means that when your "old stalwart" becomes senile, it's paired with a younger disk.
But doing that does mean rotating mirror sets when you buy a new tranch of disks. Which does put load on, which can trigger failure.
(In theory, as I don't run a storage farm) RAID6 might help here since if the disk rotation triggered a failure you'd have a second parity disk to fall back on. However ideally all the disks in an array would be from different lots.
Or, I believe that on some RAID controllers it is possible to add a third disk to a RAID1 pair, which means you could build the new disk before removing either of the old ones, thus there is never a single point of failure even during the disk replacement operation.
If you're mirroring, you should only ever mirror a "fresh, unproven" disk with an "old stalwart" disk. Doing that also means that when your "old stalwart" becomes senile, it's paired with a younger disk.
But doing that does mean rotating mirror sets when you buy a new tranch of disks. Which does put load on, which can trigger failure.
Anyone have a good plan for doing this?