grub can't read zpool
This weekend I had a small problem with my omnios installation. The installation is now more than a year old and back then, the feature flags for zfs were really fresh. So as time went on, zfs got better but somehow it was missed to update the grub installation. When I then booted my server on friday, I did not get up again as grub was unable to load my zpool.
Thanks to Rich Lowe from illumos project the bug got fixed. But I had to somehow run installgrub on my system to get it up again. For that to work, I had to find a system which either boots a current illumos kernel or lets me enter a kernel paramter.
To make things more complicated, the current omnios installation medium did not like my system and just rebooted with a kernel panic without me having a chance to get my kernel paramter from the zpool. FreeBSD 9.1 was not able to read the zpool because of the feature flags. After half a day of try and error I just went with SmartOS and lo and behold - it worked!
So I imported my zpool with
zpool import -o /mnt rpool, read my menu.lst to get the parameter and restarted with omnios to enter that command to the kernel in grub and I got a live environment up to do installgrub!
For me, the parameter in question is
-B acpi-user-options=0x2,$ZFS-BOOTFS to switch off ACPI on my Sandy Bridge Celeron system.