Well, unfortunately Filesys::DiskFree relies on the underlying df command, so you are indeed accessing a system command that the module is using on your behalf. Moreover, the docs talk about "blocks" when talking about the set method, and "bytes" everywhere else.

At the moment I can test it just on Linux and Solaris 9, so I can't tell if it always returns sizes in bytes or if it returns sizes in blocks on some OS. Could anybody please test it on some other platform and tell me if it returns blocks instead of bytes somewhere?

Thanks in advance