Host id is needed because ZFS writes it to the pool when it’s imported so that no other machine can mistakenly import the pool until this machine has exported it. This does mean that unclean shutdowns leave your pool in a state that requires other machines to use -f to import the pool. But it helps make sure you haven’t imported the pool in the wrong place, or attempted to import a pool that’s already imported by another system. It’s mostly an enterprise level feature really.
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