M p unknown unknown /dev/dsk/c1t1d0s4 << bad disk
M p unknown unknown /dev/dsk/c1t3d0s4 << bad disk

Note in your metadb - looks like someone added to the metadb but never rebooted - that's usually why you get the unknown in the status although it's possible you are also getting it because the disks are bad. The good thing is that there are so many copies of the metadb - so you can replace the bad disks without no worry about losing anything.

As far as the bad disk, get the replacement disk drives and you can use the metareplace command. Or you can use metadetach and metaclear to remove them from the metastat and replace the drives, format, and readd them. You can hot swap the drives so you should not need any down time.

Also, insure that the boot device is c1t0d0s0 and not c1t1d0s0. You don't want to hot swap or remove the drive you are booted off of (inital boot will be off one drive and then the mirrors come into play). Just check the output of eeprom and look for boot-device - hopefully it isn't simply "disk:a" but gives you the output that you would be able to tell which drive it really is. If not, then you can play it safe and reboot into single user to do the drive replacements. More info can be found in this thread