Best practice for setting up disks for ZFS on NetBSD

[David Brownlee <abs%absd.org@localhost>]

What would be the best practice for setting up disks to use under ZFS
on NetBSD, with particular reference to handling renumbered devices?

The two obvious options seem to be:

- Wedges, setup as a single large gpt partition of type zfs (eg /dev/dk7)
- Entire disk (eg: /dev/wd0 or /dev/sd4)

(I'm going to skip disklabel partitions as they are size limited and
also encounter other issues with zpool import)

Creating disks with single zfs wedges has the advantage of marking
each disk as "hey, zfs in use here", so it should be less likely to
accidentally overwrite it with something else, the wedge layer is
light enough to not add any measurable overhead, and providing the zfs
partition is aligned correctly zfs should be getting close enough to
"the real disk"

Using the entire disk seems simpler, and the system (including tools
like iostat) are not suddenly cluttered by (in this case) a set of
unnecessary dk entries.

In the event of disk renumbering both are thrown out, needing a "zfs
export foo;zfs import foo" to recover. Is there some way to avoid
that?

David