It's a neat feature for SOHO-type users, and takes advantage of the fact that the RAID layer knows about the FS. The first implementation that I know of is Drob

It's a neat feature for SOHO-type users, and takes advantage of the fact that the RAID layer knows about the FS. The first implementation that I know of is Drobo's filesystem. Asymmetric RAID is probably the only config that I'd like to see in ZFS - being able to have (say) an 8TB drive and two 4TB drives, and have 8TB of mirrored space is quite nice when you're just buying commodity kit and don't want to have to retire/match drives all the time when growing mirrors.