readynas duo removing one disk

All you actually need to do is remove it. The duo will put the volume in a "degraded" status - and it will stay in that state forever. It's best to pull the parity drive (which is normally drive 2).

Given the price of new 2 TB drives ($60-$70 street price in the US), I wouldn't do this myself.

Nor would I.
Is the data on the duo backed up, or would you be happy to lose it?

vandermerwe wrote:
Nor would I. Is the data on the duo backed up, or would you be happy to lose it?

Thanks for that, It's backed up regularly

JohnWB wrote:
Thanks for that, It's backed up regularly

If you don't care about RAID protection, your other option is to rebuild the duo in flexraid/jbod.

The process requires a factory reset.
(a) save the config, note any add-ons
(b) reset with one disk in place (can be done from either frontview or the boot menu).
(c) choose "flexraid" and RAID-0 via RAIDAR within 5 minutes or so of the reset.
(d) reinstall the add-ons (the order matters for this step!).
(e) restore the config
(f) restore data from the backup.

This would allow you to add a second disk (its own volume) later on, and increase the storage of the NAS up to 4 TB if you wanted.

This of course can be done at your convenience (e.g., you could pull the parity drive now, and reconfigure as jbod when you need the storage).

I've rebuilt my own duo as jbod - at this point it is only for backup, and I needed the space more than the RAID protection.

I wanted to repurpose a 2TB drive myself and I thought that removing it would have my 516 just rebuild, but it's still in Degraded state. Is there no way to force a rebuild?

No.

So the only way to have the RN rebuild an array is if the drive were to experience a hardware failure? Or even then would it expect that you would replace that drive with a new one?

Yes on the sparc units there is no way from the GUI to force volume rebuild. You could probably do it using linux commands and ssh.
Later readynas units have faster processors which make scrubbing feasible.

I'm on a 516. Do I just need to kick off a scrub to get it back to normal with one less disk?

No, I meant that is effectively a way to force a volume rebuild. You can't force it to change from a 2 disk volume to a single disk volume.