Is there an alternative to the illumos native fdisk? Yes, for example, GPT fdisk from Rod Smith. It includes the gdisk, cgdisk, sgdisk, and fixparts programs. Site mentions only usage on Linux, FreeBSD, Mac OS X and Windows, but it is possible that GPT fdisk may be suitable on illumos-based distributions. It requires popt library (OmniOS contains it) and latest version built with no problems, except for a small fix for ncurses.
root@test:# ./gdisk /dev/dsk/c2t3d0p0 GPT fdisk (gdisk) version 1.0.0 Partition table scan: MBR: protective BSD: not present APM: not present GPT: present Found valid GPT with protective MBR; using GPT. Command (? for help): p Disk /dev/dsk/c2t3d0p0: 10485760 sectors, 5.0 GiB Logical sector size: 512 bytes Disk identifier (GUID): F24F914A-AD82-D84D-B0FC-81351563B356 Partition table holds up to 9 entries First usable sector is 34, last usable sector is 10485726 Partitions will be aligned on 1-sector boundaries Total free space is 222 sectors (111.0 KiB) Number Start (sector) End (sector) Size Code Name 1 256 10469342 5.0 GiB BF01 zfs 9 10469343 10485726 8.0 MiB BF07 Command (? for help): i Partition number (1-9): 1 Partition GUID code: 6A898CC3-1DD2-11B2-99A6-080020736631 (Solaris /usr & Mac ZFS) Partition unique GUID: F9BEC73D-23D3-C168-E74A-D60ED3EC565D First sector: 256 (at 128.0 KiB) Last sector: 10469342 (at 5.0 GiB) Partition size: 10469087 sectors (5.0 GiB) Attribute flags: 0000000000000000 Partition name: 'zfs' Command (? for help): b back up GPT data to a file c change a partition's name d delete a partition i show detailed information on a partition l list known partition types n add a new partition o create a new empty GUID partition table (GPT) p print the partition table q quit without saving changes r recovery and transformation options (experts only) s sort partitions t change a partition's type code v verify disk w write table to disk and exit x extra functionality (experts only) ? print this menu Command (? for help):