It performs as well as any other file system, but ZFS shines when you are IO bound as compression really helps when you do sequential scans.

I have also tested ZFS with Microsoft SQL Server by exporting a ZVOL over iSCSI(FreeBSD) over 10G ethernet. But without compression as it has no benefit on 4k blocks. Performance was similar to what you would get with the same drives striped on Windows Server 2012. The big win here is of course ZFS's data checksumming. Not sure about snapshot as backup though, I need to figure out how to talk to the Windows SQL Writer Service so it can tell SQL Server to flush and lock so I can take a consistent snapshot. Microsoft really needs to improve their documentation, because this would be really helpful for several enterprises when it comes to backup speed.