I had bad experience in a disaster scenario mirror system disks, and didn't want rpc running, so I wrote a cpio script to do the same. Although it would only run one a day and you could lose 1 days changes, system disks don't usually change much and you have the major advantage of being able to recover with a "boot disk8" or whatever. The backup disk can easily be moved to another machine too.
The script is available at: www.boran.com/security/sp/solaris/mirror_boot.sh
This new version also works on Intel Solaris too.
Comments, feedback on the idea and the approach are welcome.