$ mkboot /dev/dsk/c2t6d0
There appear to be non-boot logical volumes on this device.
Overwriting them could destroy all the data on this device
Should the logical volumes be overwritten [y/n]? y
because PV isn't marked as bootable. pvcreate -B /dev/dsk/c2t6d0
PV belongs (or thinks it does) to a volume group already. (tread lightly here!):
Fix by using the -f (force) option: pvcreate -Bf /dev/dsk/c2t6d0