Disk attempted to add is too small with an Identical disk??

Well, it turned out that before I could attempt an experiment on my NV+ which has a volume that is not important, I wound up experimenting with my primary NAS, my NVX BE. It has 2xHitachi 3TB drives and 2x1TB Seagate ST1000528AS drive (bays 3 & 4). The drive in bay 4 has been throwing SMART errors for a while and over night they increased form 278 to 334, where previously they increased by about 6 each time. I had a spare ST1000528AS sitting by, so I hot pulled drive 4 waited for the response from the system and then hot added the spare. It checked the drive and said it passed, but never started the resync, so I knew something was wrong. Checking the logs, the drive was "too small".

So, I shut the NVX down, removed the three good drives and then did a factory default on the "too small" drive. After it initialized and created the one drive volume, I shut the NVX down, removed that drive and put the three good drives from the array back in, and rebooted. After it booted, and was back on line (I was getting the message from the NVX that C: was unprotected) I then hot added the drive that it had said previously was too small. The NVX rejected the drive again as too small.

I pulled another ST1000528AS from the cabinet (I have a total of 10, 3 of which were spares), hot added it. It passed and the NVX started the resync process. Apparently, when a drive is "too small" even if the same brand and model (even in my one case of sequential serial numbers) there is truly something different about the drives. While it may take one of the Jedi who have been doing these tests for years to confirm, but my suspicion is that even if it is one sector smaller than the previous smallest drive, it will be rejected.