IBM 6C4 - Manual (Page 129)

To use the Erase Disk option, specify the number (0-3) of patterns to be written.
The patterns are written serially; that is, the first pattern is written to all blocks.
Then the next pattern is written to all blocks, overlaying the previous pattern. A
random pattern is written by selecting the Write Random Pattern option.
Note: The Erase Disk service aid has not been certified as meeting the
Department of Defense or any other organization’s security guidelines.
To overwrite the data on the drive, use the following steps :
1. Select Erase Disk.
2. Do a format without certify.
3. Select Erase Disk to run it a second time.
For a newly installed drive, you can ensure that all blocks on the drive are
overwritten with your pattern if you use the following procedure:
1. Format the drive.
2. Check the defect MAP by running the Erase Disk selection.
Note: If you use Format and Certify option, there may be some blocks that
are placed into the grown defect MAP.
3. If there are bad blocks in the defect MAP, record the information presented
and ensure that this information is kept with the drive. This data is used later
when the drive is to be overwritten.
4. Use you drive as you would normally.
5. When the drive is no longer needed and is to be erased, run the same version
of the Erase Disk selection that was used in step 2.
Note: Using the same version of the service aid is only critical if any bad
blocks were found in step 3.
6. Compare the bad blocks that were recorded for the drive in step 3 with those
that now appear in the grown defect MAP.
Note: If there are differences between the saved data and the newly obtained
data, then all sectors on this drive cannot be overwritten. The new bad
blocks are not overwritten.
7. If the bad block list is the same, continue running the service aid to overwrite
the disk with the chosen pattern(s).
Chapter 6. Introducing Tasks and Service Aids 111