Reallocated sector count continues to climb

A lot of this depends on the rate of accumulation of reallocated sectors. For example if you only have a dozen or so after 100 days and the count is not going up by a dozen or so every day, then I would say continue to use the drive. If the rate is already fairly high and increasing rapidly, I would say have a spare drive handy.

On the other hand, if you can return the drive to the vendor for replacement as a defective drive I would do so. When you RMA a drive to a manufacturer, they do not send you a brand new drive, they send you a refurbished drive of the same model if they have one. If they do not have one, then they may send you one of the same capacity which may not be on the HCL, or they may send you a drive of a higher capacity.

Over the past four years, I have had occasion to RMA two drives to Seagate. The first died about 45 days after setting up my NV+ almost four years ago, it just died. I RMA'd the drive, but also bought a brand new on to match the other drive in my array and get redundancy back. It took about 5 days for the drive to get to Texas (where RMA drives go), one day to check out and 3 days for the replacement to arrive. If was a refurbished 750GB drive that I have used ever since as a backup target for my NAS. This past summer, I lost a second Seagate, this one a 1TB drive out of my second NVX (backup target), again it just died, no warnings. The RMA experience was about the same, except this time the drive I received was the same model as the one I sent in, and even the same firmware version. I may use it in the backup unit, but not in my primary unit.

It is not recommended that you use refurbished drives in a RAID array. Although in a RAID composed of consumer drives rather than the much more expensive enterprise drives (as found in business units) they may not make that big a difference. After all a refurbished drive has been subjected to quality testing before being sent out, something no longer done on the original factory lines.