> ZFS was the thing that convinced me that layering isn't actually always great and sometimes vertical integration makes sense. The funniest thing is that ZFS

> ZFS was the thing that convinced me that layering isn't actually always great and sometimes vertical integration makes sense. The funniest thing is that ZFS is layered. It's just that 99% of people only see the final result, and don't notice the one place the abstraction leaks a little (zpool and zfs commands operate on separate layers with a bit of overlap). ZFS is composed of separate layer for actual block devices, a layer of object-storage system on top of it called DMU (those two layers overlap a bit in handling data safety), and finally on top of the object storage there is implementation of posix-compatible filesystem called ZPL, an emulation of plain block storage called ZVOL, and there is optional LustreZFS which also operates on that layer. There's a bit more segmentation when dig deep into code (whole special I/O scheduling and processing system called ZIO, for example, which provides things like encryption and compression) but yes, ZFS as a whole is quite layered - just with different APIs in between than offered let's say by Linux (you could technically build ZPL on top of now removed SCSI object storage driver, for example, but it would lack things)