This is all bad advice and I appreciate trurl and itimpi for advising others to not follow in my footsteps. Turns out the root cause of most of my issues was that I needed to update my bios
I'm facing this issue now. Digging through the diagnostics the original issue seems to be that I used a tool to download files and the file names were too long. That borked my Docker btrfs and I've been having issues ever since.
As for the resource busy issue. When I run `lsblk /dev/sda` it points to `/dev/sda1` which points to `/boot`
I unmounted `/boot` with `umount -l /boot` but then I got stuck again. Some digging brought up a post on unix.stackexchange answered by ZakW that advised me to read the contents of `/proc/mounts` with `cat /proc/mounts`. Reading through `/proc/mounts` showed me that `/mnt/cache` is actually the mount point for my device and not the device "name" (not sure about that terminology).
`lsblk /dev/nvme0n1p1` pointed me back to `/mnt/cache` and with no other clues what to do I took a stab in the dark and unmounted `/mnt/cache`.
Finally I was able to run `blkdiscard /dev/nvme0n1p1`. I realized after the fact that I didn't run it on `/dev/sda` and once blkdiscard finished I tried running it on `/dev/sda` but I got the busy error again.
I rebooted my unraid box and when it came back up it showed the cache as missing a file system. On the "Main" tab I had the option to format the cache drive and everything looks good so far.