Does anyone know if it is possible to use bcache for an already existing BTRFS array that is already filled up without having to reformat the bcache array?
I already have a BTRFS array with 5 drives (created using mkfs.btrfs -d single) and I just want to add a read cache using an SSD. Unfortunately at the time I created the BTRFS array I didn’t realize that in order to use bcache you have to preformat the backing device (bcache terminology for the device you want to cache). The array is now unfortunately completely filled with data.
There seems to be an already existing tool on github (g2p/blocks) but its pretty ancient. For example it says that it needs btrfs-show-super however according to btrfs man page that tool doesn’t even exist anymore (i.e. its now btrfs inspect-internal dump-super). I am also running Archlinux/Manjaro and some of the referenced packages don’t appear to exist (or its unclear if there are equivalents). From what I have read (can’t paste links) apparently the reason why its not easy to use prexisting filesystems is because of a superblock that needs to be placed so that bcache can prevent the user from directly accessing the backed device which would corrupt the cache however this only appears to be a concern if have a write/read cache (in my case I only want a read cache, array is already filled anyways).