I am currently on UnRAID 6.9.1. My server is currently using 1 of my 2 2TB NVMe drives as in the cache pool. Up until this point, the second NVMe drive had been sitting around as an unsigned drive. My initial intention for the second drive was to have it be a dedicated Plex meta drive. However, once I learned that the Plex docker container stores the Plex metadata folder on the cache drive by default I figured I may as well merge the second NVMe SSD into my cache pool. But for whatever reason when I try to add the spare drive to my cache pool the total size of the pool does not increase to 4TB. It continues to show 2TB. I’m not sure why this is. I have tried removing and re-adding the drive to the cache pool only for the issue to persist. Any ideas? 

The default btrfs profile when you have 2 drives is raid1 (for redundancy).    In a 2 drive pool this gives the space of the smallest drive as the available space.  If you want additional space rather than redundancy then you need to switch to a different profile using the procedure described here in the online documentation accessible via the ‘manual’ link at the bottom of the unRaid GUI.

Thanks for the info itimpi. If that's the case I'll just leave the spare NVMe unassigned for plex.

1 hour ago, Chukwuka13 said:

Thanks for the info itimpi. If that's the case I'll just leave the spare NVMe unassigned for plex.

Since you are on 6.9.1 you might want to put it into its own pool rather than using it via Unassigned Devices.

That's a good point. With the multi pool feature in UnRAID 6.9 is there any benefit to keeping the unassigned drive plugin around?

14 minutes ago, Chukwuka13 said:

That's a good point. With the multi pool feature in UnRAID 6.9 is there any benefit to keeping the unassigned drive plugin around?

The UD plugin is what you will need to use for drives that are not always plugged in.    In addition the UD plugin can handle hot-plugging drives while unRaid cannot for pool or array drives.

Okay that makes sense. In my case, past the initial migration to UnRAID I don't foresee myself attaching any temporary drives to my server. I guess it wouldn't hurt to keep the plugin around just in case.