@ScottPSilver Re:
Pool not mounting is the issue here: it seems. Poorly pools don’t mount without custom mount options.
And without a mount btrfs can tell us little about what is wrong. Take a look at our following doc:
https://rockstor.com/docs/data_loss.html
It has a number of relevant sections to your requests. Also if no mount found to be possible, which could only be concluded once you have also followed for example:
https://rockstor.com/docs/howtos/stable_kernel_backport.html
And tried the newest recovery mount options: there is always:
https://btrfs.readthedocs.io/en/latest/btrfs-restore.html
One problem with you receiving assistance on this issue is the bouncing back and forth with your other thread:
And the numerous drive sales links 
. I think they are best removed as it tends to cloud things and age threads quickly.
So in short: take a look at our above linked HowTo and research your mount options. As you do now seem interested in refreshing/updating a backup: and want to jump to whole pool repair first it seems: then you need a to aim for a read-write capable mount option. Read-only is far easier to achieve for data retrieval purposes as poorly btrfs pools will go read-only (ro) to protect data integrity. But one needs a read-write mount to be able to run a scrub: the go-to repair procedure that can seek-out failing checksums and replace the associated data/mettadata with the still good ones (if hey can also be found).
Hope that helps.