Nevermind, I stumbled upon RAID-1 for boot drive - #17 by gibmat which put me on the right track.
The correct format for incus admin os system storage edit was (full excerpt):
config:
scrub_schedule: 0 4 * * 0
pools:
- name: local
devices:
- /dev/disk/by-id/nvme-PC711_NVMe_SK_hynix_1TB__KNA8N42181070865T-part11
- /dev/disk/by-id/nvme-PC611_NVMe_SK_hynix_1TB_CD07N8499102Y832V
type: zfs-raid0
Nothing more, nothing less.
scrub_schedule is needed, as well as being outside of a state key.
After that my second drive was instantly added to the pool and all works well ![]()
Would you be so kind as to update the documentation in Expanding the “local” storage pool - IncusOS documentation with this information whenever you have the time?
Thanks!