Приведу цитатой, которую нашёл в рассылке по Illumos
the boot disk(s) have fdisk partitions to support boot, and on install you get special fdisk partition labeled as «solaris2» (there is/was also «solaris», but linux stole it and using for linux swap). fdisk partitions have names suffixed as pX, where X has values from 1-4 for primary partitions, p0 is special case to indicate whole physical disk.
inside solaris2 fdisk partition you have SMI label with slices — on x86 there are total 10 slices (0-9), device names are suffixed as sX, X with values from 0-9. for historical reasons, slice 2 is «special», labeled as «backup». it’s defined to cover all the available space seen by SMI label (full disk in case of sparc, fdisk partition in case of x86). today slice 8 is to mark space for partition boot block and slice 9 is not usable.
so, today, if you get fresh install, you see slice 0 starting from cylinder 1, and slice 8 defined to start from cylinder 0. this is needed to make sure the rpool wont overwrite partition boot block (grub).
now, there is new kid in this game, called GPT label. whenever you create pool by using disk name ending with dX (X is 0 for physical disks and lun number for raid luns) and skipping the sX or pX, the zpool command will label the disk for you with using GPT (or EFI) label. current opensolaris based systems cant boot from such disks, only solaris 11.1 can boot from GPT labeled disks. so, to use such disk for booting, you need to remove GPT label and replace it with «normal» fdisk + SMI. to do that, you start format -e (expert mode), select your disk, run fdisk from it to delete fdisk partitions if needed, and from format prompt use label command to write down new label. you will be asked to select from SMI or EFI label type, select SMI. after that you can create correct fdisk partitioning first and then create SMI slices using format — partition menu (or prtvtoc | fmthard ).
once we get to the point we have boot loader capable of using GPT labels, we can forget all this fdisk madness, but till that time, its the way you have to deal with it.