Cache-like drive when the main drive is offline

Hello everyone.
I have a RaspberryPi as a nextcloud server. In this device, i have a small 64GB usb drive (A) and a 2TB HDD on a usb adapter (B). This HDD constantly spins and this wastes energy for the amount of usage that it gets.
What i want to do is setup the server with the A device receiving the files whenever the B drive is offline. When the B drive is online, the files cached on A goes to B.
How can i setup this configuration?

Nextcloud version: 27.1.1snap.1
Operating system and version: Debian 11

Hi @cnpjoto

I don’t think that’s possible, or at least Nextcloud itself doesn’t offer such a feature. And quite honestly, even if you could get something like this running with external tools, it wouldn’t be worth to deal with the additional complexity of such a setup, and the potential issues associated with it.

A 2TB HDD is consuming about 5-6 watts. If you think that’s too much, I’d suggest replacing the HDD with an SSD. This would save around 3-4 watts of power and at the same time allow faster access times.