How do I determine how much free space is still available in a diskgroup for increasing repo sizes?

We need to increase the size of some repos but I cannot tell how much free space is still available in the containing diskgroup so that I can add reasonable amounts of storage to the repos.

For example we have X5.2 system and the DATA and RECO diskgroups are located on the 64 TB of HDD disk space.  But all the repos created in these diskgroups so far show redundancy

as "mirror" which presumably means something equivalent to RAID 1.  So we actually only have about 32 TBs of available storage.    By using

       acfsutil info fs

I have added up the used storage on the DATA and RECO diskgroups by adding the storage used by all repos and I get a figure of roughly 20.78 TBs.  So we should have about 11 TBs