From ggus ticket:

those two (damned) groups were inserted some years ago in order to fulfil a requirement by the ATLAS experiment, which wanted to keep track of files which were read or written. Basically storm changes the group ID of every file upon access with the two group 'storm-SA-read' and 'storm-SA-write'
However, for normal usage, this is not really needed, so these messages are harmless, though admittedly annoying.