Скорее всего, это связано с тем, что эти слайсы указывают на одно и то же место на диске. Скинь сюда ту же таблицу, которая у меня получилась в конце:
$ pfexec format
Searching for disks...done
AVAILABLE DISK SELECTIONS:
0. c7d0 <DEFAULT cyl 7830 alt 2 hd 255 sec 63>
/pci@0,0/pci-ide@1f,2/ide@0/cmdk@0,0
Specify disk (enter its number): 0
selecting c7d0
NO Alt slice
No defect list found
[disk formatted, no defect list found]
/dev/dsk/c7d0s0 is part of active ZFS pool rpool. Please see zpool(1M).
FORMAT MENU:
disk - select a disk
type - select (define) a disk type
partition - select (define) a partition table
current - describe the current disk
format - format and analyze the disk
fdisk - run the fdisk program
repair - repair a defective sector
show - translate a disk address
label - write label to the disk
analyze - surface analysis
defect - defect list management
backup - search for backup labels
verify - read and display labels
save - save new disk/partition definitions
volname - set 8-character volume name
!<cmd> - execute <cmd>, then return
quit
format> pa
PARTITION MENU:
0 - change `0' partition
1 - change `1' partition
2 - change `2' partition
3 - change `3' partition
4 - change `4' partition
5 - change `5' partition
6 - change `6' partition
7 - change `7' partition
select - select a predefined table
modify - modify a predefined partition table
name - name the current table
print - display the current table
label - write partition map and label to the disk
!<cmd> - execute <cmd>, then return
quit
partition> pr
Current partition table (original):
Total disk cylinders available: 7830 + 2 (reserved cylinders)
Part Tag Flag Cylinders Size Blocks
0 root wm 1 - 7829 59.97GB (7829/0/0) 125772885
1 unassigned wm 0 0 (0/0/0) 0
2 backup wu 0 - 7829 59.98GB (7830/0/0) 125788950
3 unassigned wm 0 0 (0/0/0) 0
4 unassigned wm 0 0 (0/0/0) 0
5 unassigned wm 0 0 (0/0/0) 0
6 unassigned wm 0 0 (0/0/0) 0
7 unassigned wm 0 0 (0/0/0) 0
8 boot wu 0 - 0 7.84MB (1/0/0) 16065
9 unassigned wm 0 0 (0/0/0) 0