On my T5220's I've ended up using raidctl to set up hardware mirroring for the boot drive. Then I use ZFS to pool other drives. I've stopped using SVM, or any of it's previous renditions, although I used to use it fairly extensively in Solaris 8. ZFS is just amazingly cool (and simple to use). I haven't yet tried using it for boot drive mirroring, but I did see a document on transitioning to it using luupgrade, so I have a clear path to that option.