CLEANING AND RECERTIFYING MAGNETIC DISKS

Today, the removable and interchangeable magnetic disk pack is one of the most frequently used ^{mass storage media.} Not only is it small, fast, and reliable, but with the proper care and handling, it has an almost indefinite life span. Like magnetic tape, the main enemy of the disk pack is dirt. During the manufacturing of the disk packs, every precaution is taken to maintain a sterile environment and a contamination-free assembly of each component of the disk. However, these safeguards do not entirely prevent some contamination from occurring, and everyday operation continues to increase the contamination level until data checks (read/write errors) do occur.

During normal computer use, three different types of errors are encountered on disk packs: temporary errors, permanent errors, and disastrous errors (head to disk contact or head crash).

TEMPORARY ERRORS OR SOFT DATA CHECKS- These temporary errors are the direct result of a minor buildup of contaminants, such as dust, smoke, and oil.

PERMANENT ERRORS OR HARD DATA CHECKS- These permanent errors cause data to be lost because of an excessive buildup of contaminants. As a result, the read/write heads are no longer able to access this particular area on the disk.

HEAD TO DISK CONTACT OR HEAD CRASH- These disastrous errors are caused when a read/write head of the disk drive unit comes into direct contact with the surface of a disk platter. Again, this is the result of an excessive buildup of contaminants.

These errors can be prevented by inspecting and cleaning the disk pack. Although none of the major disk pack manufacturers recommend a regular schedule for cleaning of disk packs, they do recommend that disks be cleaned and inspected when they have been exposed to possible moisture or contamination. The fact is, during operation, the disk pack is surrounded by dirt and grease particles that are circulated through the air by the cooling fans of the disk drive; consequently, there is a definite need for a cleaning procedure, if not an actual schedule. If your installation has a disk cleaner/certifier, learn how to use it, and you will find fewer disk errors and a significant decrease in the number of computer reruns. A well-organized disk management program will serve to eliminate head crashes caused by contaminants; decrease, if not eliminate, hard data checks; and decrease significantly the number of soft data checks encountered.

DEGAUSSING MAGNETIC MEDIA

Degaussing magnetic media\tapes, disks, and drums-involves a process in which you demagnetize the media itself. This rearranges all the 0 and 1 bits, sort of mixing them up, you might say. Normally, the only time you would be required to perform such an operation is when you must declassify (remove the data from) the media before the media can be scratched for reuse. To remove a previously recorded magnetic signal (all the 0 and 1 bits), use a concentrated magnetic field to magnetically saturate the oxide coating of the media and randomly orient all the magnetic particles.

Magnetic Tape Degaussing

To degauss a magnetic tape, you must pass the entire tape through controlled fields of alternating current to reduce the signal level of the magnetic tape's recordings to a level which is below the capability of ADP equipment to interpret. This requires that signal level reduction be performed on the entire reel of magnetic tape, including the tape leader and tape trailer.

For a tape 1 inch or less in width to be considered unclassified by the National Security Agency (NSA) standards, the signal on the tape must be reduced a minimum of 90 dB (decibels) below saturation level after degaussing. The manufacturer's recommended operating procedures should be followed when degaussing a tape. Also, the tape degausser should be checked at least quarterly by technical personnel to ensure proper operating level specifications.

Before degaussing a tape, you should remove the tape wrap-around strap to prevent the reel from jamming, and secure the end of the tape with a foam rubber stopper to prevent the tape from unwinding. The degaussing operation itself takes no more than 2 minutes per reel for a magnetic tape with a maximum one-inch width.

Magnetic Disk, Diskette, and Drum Degaussing

Rigid magnetic media such as disk and drum storage, as well as diskettes (also known as floppy disk), should be machine cleared (overwritten), using a specially designed computer software program. Once the media has been overwritten, it should be verified (checked) to be sure the read mechanism cannot detect any traces of data information except the characters used in the overwrite procedure. Only then can the media be considered as unclassified, and all classification labels and markings identifying the subject matter be removed. You should also ensure the computer operator checks out the computer and all related components that are to be used immediately before beginning the overwrite procedure. This is to let you know that malfunctions, which could prevent the classified information from being effectively overwritten, do not occur. During the overwriting process, all storage locations will be overwritten a minimum of three times, once with the binary digit "1 ," once with the binary digit "0," and once with a single numeric, alphabetic, or special character (other than "0" or "1"). The current used in overwriting must be equal to that used when the data was first recorded, but not so strong that it will damage or impair the equipment. If the storage device fails in such a reamer that it cannot erase the data from the media, the media may be declassified by exposing the recording surface(s) to a permanent magnet having a field strength at the recording surface of at least 1500 oersted. Care must be taken to ensure that the entire surface is wiped at least three times by a nonuniform motion of the magnet. Care must also be taken to assure that all tracks are covered by the center of the magnet. A thin sheet of clear plastic (a 1-to-5-mill sheet) should be used to prevent any damage to the recording surfaces.