It is ZFS, and is on by default. ZFS also offers gzip compression, and you can "turn up" the LZ4 from the default if you wish. I've almost always left it at th

It is ZFS, and is on by default. ZFS also offers gzip compression, and you can "turn up" the LZ4 from the default if you wish. I've almost always left it at the default; on my home file server (slightly long-in-the-tooth 6 core xeon, enterprise-grade spinning rust), throughput is noticeably faster on compressible data. (ZFS dedupe should only be considered for weird cases, like if you somehow have a ton of RAM but very limited storage. Frankly, at this point I think it is an attractive nuisance that leads beginners down a dangerous path and should be removed, or at least the commands to enable it should be given loud, scary confirmation messages.)