Thanks so much for this info, I've been desperate to implement compression on my huge collection of Sony RAW image files.
I copied across 20GB of files as a test and my compsize output looks like this:
Processed 568 files, 32187 regular extents (32187 refs), 0 inline.
Type Perc Disk Usage Uncompressed Referenced
TOTAL 86% 16G 19G 19G
none 100% 15G 15G 15G
zlib 25% 948M 3.6G 3.6G
I think it's saying that the folder is 86% of what it was, i.e. it's 16G on disk rather than 19GB which is the uncompressed size. Is that correct?