Explanation/Reference:
A: ZFS is the default root file system.
UFS is a supported legacy file system, but it is not supported as a bootable root file system.
E:
If your system has more than one OS installed on the system or more than one root boot environment in a ZFS root pool, you can boot from these boot environments for both SPARC and x86 platforms:
* Starting with the Solaris 10 10/08 release for a SPARC based system, you can boot a ZFS root file system in a ZFS pool. For ZFS root pools, you can list the available boot environments with the boot command with the -L option. You can then choose a boot environment and use the OBP boot command with the -Z option to boot that boot environment.
* Starting with the Solaris 10 1/06 release for x86 based systems, a GRUB boot menu provides the interface for booting between different boot environments.
Note:
* The name originally stood for "Zettabyte File System" but today does not stand for anything.
Incorrect:
Not C: Mirroring is not enabled by default.
Not D: Alternate boot environments
If you want to create a backup of an existing boot environment, for example, prior to modifying the original boot environment, you can use the beadm command to create and mount a new boot environment that is a clone of your active boot environment. This clone is listed as an alternate boot environment in the GRUB menu for x86 systems or in the boot menu for SPARC systems.