ZFS includes inline compression, meaning files are compressed and decompressed on the fly. Save for highly-compressed files like video, I’ve always left the compression algorithm as the default, which for years has been lz4 . I interrogated this dataset holding my books with the requisite zfs commands:# zfs get compression zten/books ==> NAME PROPERTY VALUE SOURCE ==> zten/books compression lz4 inherited from zten # zfs list ==> zten/books 42.7G 601G 42.7G /zten/booksSo about 42.7 GB of books compressed with lz4 . In my experience, it’s hard to go wrong with any of ZFS’s compression options. gzip does give better compression, and the difference between loading a PDF from a dataset using gzip over lz4 was imperceptible to me.