I would just like to correct os2mac, that zones can indeed be used as physical resource limitation.
As per document : http://www.oracle.com/technetwork/da...wp-1911914.pdf
If you use resource pool with processor sets attached to specified zones, Oracle recognizes it as hard partition for software licensing.
As for LDOM and high availability you can use migrate option and/or import the ldom configuration on another server manually (this will require FC or ISCSI disk for root available to multiple nodes).
Other option is to have, for instance, two LDOM on local disks with zone inside on FC/ISCSI disk.
If one host goes down, you can always attach and boot the zone(s) on another LDOM (node).
Since zone fc zpool now will warn you that the zone/zpool is active on another node(LDOM), you will not be able to accidentally attach the zone on both LDOM as the same time.
And of course you can always buy Solaris cluster which will do above things for you with HA agents (but that's rather expensive).
Hope that helps