On more than one occassion now, I have run into problems where the Solaris boot archive wasn’t in a consistent format at boot time. This stops the boot process, and the console recommends booting into FailSafe mode to fix it. If you want to do this manually, you can run the bootadm utility with the update_archive command, and the location where the root file system is mounted:
$ bootadm update_archive -v -R /a
I am hopeful that the opensolaris community will enhance the archive support to make it more fault tolerant. The current code seems somewhat brittle.