Or, you find that a drive in your RAID array fails and you can no longer get a drive with the exact same model and disk geometry as the other disks in the RAID

Or, you find that a drive in your RAID array fails and you can no longer get a drive with the exact same model and disk geometry as the other disks in the RAID What RAID controllers require replacement drives with the exact same model and disk geometry? I've not seen one that wouldn't take a bigger drive as a replacement.