I've had many drives go bad on xpenology boxes. In every case my experience was the same, shut down, replace the drive, boot back up, go to the disk management UI, and repair the affected array. The UI will ask which free drive to apply to the task, select your new drive, and it'll do it's thing. Your data is available in the meantime but the system will spend approx 12 hours rebuilding. This will cause it to miss it's next scheduled shutdown if it conflicts with the rebuild, FYI. I've never had an SHR, I've always used RAID 5, but I would expect your experience to be the same.
Alright I resolved the issue with a BIOS firmware update to the motherboard. A huge pain because I don't have Windows, so I had to use a USB pen drive to install Win10 to a spare drive, then use the @BIOS utility. Anyway.
Thanks so much @flyride, @Tensol and @sbv3000. Your suggestions and patience were very helpful. Cheers.
