I'd say it's more complicated even for simple ZFS pools without any redundancy or fancy features. My favorite illustration on this topic would be figure 2 from

I'd say it's more complicated even for simple ZFS pools without any redundancy or fancy features. My favorite illustration on this topic would be figure 2 from "Reliability Analysis of ZFS" (PDF): http://pages.cs.wisc.edu/~kadav/zfs/zfsrel.pdf http://pages.cs.wisc.edu/~kadav/zfs/zfsrel.pdf I still miss some of the features that are hard (if not impossible) to replicate in layered storage systems, like Merkle tree checksumming, but near-nightmare that low-level debugging of ZFS was actually turned me away from that filesystem.