That sounds backwards. Don't you have to manually define the layout of the vdevs first in order to establish the redundancy, and then allocate the volumes you use for filesystems or iSCSI? If you just do a `zpool create` and give it a dozen disks and ask for raidz2, you're just creating a single vdev that's a RAID6 over all the drives. There's an extra step compared to the btrfs workflow, but if you're not using that opportunity to micromanage your array layout I don't see why you'd prefer that extra step to exist.

> and I can't have multiple file systems (well, you can have sub-volumes but you can't avoid a big file system in that collection of devices).

Isn't this a purely cosmetic complaint? With at least btrfs, you don't even have to mount the root volume, you can simply mount the subvolumes directly wherever you want them and pretty much ignore the existence of the root volume except when provisioning more subvolumes from the root. You can pretend that you do have a ZFS-style pool abstraction, but one that's navigable like a filesystem in the Unix tradition instead of requiring non-standard tooling to inspect.