If you try to boot ZFS on certian HP servers, and apparently various other machines, gptzfsboot reports errors:
error 1 lba 32
error 1 lba 1
No ZFS pools located, can't boot
This can be worked around by reading the ZFS pool from a disk other than the one that was booted from.
This patch retries the boot disk, with 'secondary disk' settings, if reading from it fails the first time.