As @phillxnet said its pretty easy. Thanks @phillxnet for the help on previous issues btw!
I have successfully imported a BTRFS array from my old ubuntu server into RockStor. You must set a label for the BTRFS storage BEFORE importing.
btrfs filesystem label /dev/sdx [newlabel]
Any subvolumes created before hand will be imported as Shares. After the subvolumes are created you can do
cp -Rv --reflinks=always /some/source /some/destination
to copy files into the new subvolume and not make a duplication of all the data as all that command does is essentially link to the data location on the HDD…
Hope that helps!
Dylan