Linux does not support mounting a Journaled HFS+ volume read/write, at least not safely.
As Mac OS X by default (for many years now) has formatted HFS+ volumes with journalling enabled, this is a problem.
If it is an external data drive (for Movies etc) that you need to move back and forth between the Pi and a Mac you could format it as HFS+ without journalling and it should mount read/write. (I have not tested this however)
Or you could use EXFAT / FAT32 which are supported for read write fo…
I think the problem I ran into with EXFAT and FAT32 was they don’t support files >4GB. I’ll try formatting the drive without journalling and report back.