I'm on unRAID 7.2.x. I had 2x cache drives. 2 SSDs of size 256 GB (sdb) and 250 GB (sdc) respectively. 256 GB (/dev/sdb) is failing from a hardware standpoint.

I have a spare 1 TB SSD (sdd). I throw it in and added it to the cache pool. It's now part of the BTRFS pool.

I have the data from /dev/sdb1 copied and backed up. I need to drop /dev/sdb entirely, but I cannot since BTRFS complains about "Too many wrong or missing drives".

One solution said I can convert the BTRFS pool from Single to RAID1, but I can't find where to do this. Most of the documentation appears to be for unRAID 6.x.

I'm not sure what information I need to provide to you all in order to help me out.

I've now changed all Shares that were set to Cache to now be Cache -> Array. I've started the mover, but it's ridonculously slow. About 100 MB/minute. But it's moving.

The only one I'm not sure of is my docker.img file which is at /mnt/cache/docker.img. Since it's not a share, I figure I'll have to stop docker, move the image, update the location, then start docker again.

Mover can be slow when moving lots of small files, but it will do the job.

docker.img will need to be moved manually, or you can just recreate it.

Yes, I have everything migrated off, so the cache drive is now sitting idle. I just have no idea how to terminate the cache pool so I can recreate it.

You can create on the pool device and then "remove pool", then add the new one.

JorgeB, I apologize. Can you explain what you mean when you say "create on the pool device"?

I meant you can create a new pool with the new device, after removing the old one; just click "add pool"

That's the problem. I can't remove the old one. I have no option to do so. I can't remove a drive from the existing cache pool, either.
Or more specifically, if I CAN do it, I don't know how.

To remove a pool, click on the first pool device and then "remove pool"

Holy crap. I have no idea how I didn't see that in the past...