Let's use the shiny ZFS to have a mirrored pool which we can use to boot in case one of the hard disks fails. This involves several steps :
Install a second disk in your box :)
format the disk so that we can actually use it
make it the same layout as the disk we already run on
attach it to the pool in question
Now point (3) and (4) need some explanation since I'm experimenting with the root pool (nothing better than a little thrill not being able to boot if things go wrong) and my computer uses the good old BIOS it cannot boot EFI labeled disks. For this reason I have to use slices, I'll probably rip out some old storage box in the next weeks and see how much of this process is left when using whole disks.
I assume you are indeed capable of physically installing a second, third or nth disk in your computer so let's jump to point (2).
Formatting the disk(s)
Simply use "format" :)
No go "fdisk" it and delete all the partitions on the disk. Then create a new partition, make it a Solaris partition and be done with that part.
Duplicate the disk layout on both disks
Now OpenSolaris provides us with 2 nice tools to make one disk have exactly the same layout as another disk. Use them like below:
Attach it to the pool in question
Let's have a quick look at the existing pool:
Nice we now see what our original device name is and what our pool name is, we need both for the next command. Remember in my example the new disk slice (the BIOS vs. EFI thing) is c8t2d0s0. We should be all fine to attach the slice to the pool and see it start recovering.
Ouch, didn't quite work, so let's do as instructed, and right thereafter let's investigate the staus of the pool:
Looks all nice, now let's do the grub stuff so that we can boot from both disks:
A last check on the status of our pool:
To my untrained OpenSolaris eye this looks all nice and shiny now.