from the sun manual, and from oracle: http://www.oracle.com/technetwork/server-storage/solaris/overview/purge-135585.html
Use format(1M) and select the disk you wish to erase. Enter the defect, and primary commands to read the manufacturer's defect list, and update the in-memory defect list. Then use quit to get back to the main menue:
format> defect defect> primary defect> quit
Go to the the analyze option. Enter the purge command and, when prompted, specify a slice that encompasses the entire disk(usually slice 2, but you should verify this manually - see 1005824.1 for more information). This will take a very long time, but, many disks can be purged simultaneously, if desired. When the command returns, go back to the main menue by entering quit:
format> analyze analyze> purge ... analyze> quit
Repeat the above steps to purge both the manufacturers', and the grown, defect lists:
format> defect defect> both defect> quit format> analyze analyze> purge ... analyze> quit format> quit
What It Does
The purge command writes four patterns to the entire surface of the disk. The first three, write alternating combinations of 1's and 0's to each bit location on the surface(the actual patterns are 0xaa, 0x55 and 0xaa again). Then, purge will read, to confirm that all that data was correctly written. If all this is successful, it will do a final wite of 0x40.
This procedure complies with Department Of Defence(DOD) wipe disk standard 5220.22-M.