depot/nixos/doc/manual/administration/zfs-state.section.md

ZFS

When using ZFS, /etc/zfs/zpool.cache should be persistent (or a symlink to a persistent location) as it is the default value for the cachefile property.

This cachefile is used on system startup to discover ZFS pools, so ZFS pools holding the rootfs and/or early-boot datasets such as /nix can be set to cachefile=none.

In principle, if there are no other pools attached to the system, zpool.cache does not need to be persisted; it is however strongly recommended to persist it, in case additional pools are added later on, temporarily or permanently:

While mishandling the cachefile does not lead to data loss by itself, it may cause zpools not to be imported during boot, and services may then write to a location where a dataset was expected to be mounted.