CLEANING AND RECERTIFYING MAGNETIC TAPE
How important is tape cleaning and recertification? Let us answer that question by asking another question: When do you suppose tape failures are most likely to occur? If you answered, when the tape is being used on the computer system; then you are correct. Consider this example: an unrecoverable tape error appears while the operator is trying to read in reel four of an eight-reel master file; the operator is about 3 hours into a very important job, and finds out there is no way to recover (restart) the job starting with reel three of the input. A failure at this stage of the operation gets the operator and a good many other people very upset, for we all know that reruns are costly in both time and money. Such failures can be avoided if tapes are cleaned and recertified on a regular basis. It is well worth the effort to properly care for tapes according to a regular planned schedule; since this avoids upset and inconvenience and gives your users confidence that your AIS facility is running smoothly.
Careful and planned maintenance of magnetic tapes can minimize and even possibly eliminate a lot of lost computer time. The first step in every magnetic tape maintenance program is, obviously, careful cleaning. Despite the many safeguards against contamination, you can believe that magnetic tape will eventually acquire some contamination and cause read or write errors.
You will find the greatest number of tape errors normally occur in the first 100 feet of a reel. When this is the case, the appropriate action is to cut off the contaminated area, relocate the BOT reflective marker, and continue to use the tape (see figure 2-11). In most cases, the reduced length will not detract from its usefulness.
This procedure is known as stripping a tape. After a tape has been stripped five times, it should be reloaded (transferred) onto what we call a mini-reel. A mini-reel is about half the size of a standard reel of tape.
If the errors continue throughout the length of the tape, you should determine whether the errors are distortion errors or dirt errors. Distortion errors are usually the result of careless handling (abuse) of the tape and can rarely be corrected. Distortion errors can be seen as wrinkles, creases, turned-up edges, or a slight stretching of the tape. Dirt errors usually result from the accumulation of microscopic foreign matter on the tape surface and can be removed by careful cleaning. To do this, you need to use a tape cleaner.
Tape cleaning is the process of removing all foreign particles (known as residual buildup) and protruding debris from the oxide and back side (the shiny side) of the tape. This process does not destroy any of the data that has been previously recorded on the tape.
New tape has a tendency to shed oxide particles near the surface for approximately the first six passes through the read/write heads of the magnetic tape unit. Unless the new tape is cleaned at least twice, increased tape unit head wear could result. You will also find that deterioration of the edges of the tape is the major cause of most tape-generated debris. Edge guides that help to direct the tape along the tape path also cause a constant edge-scuffing. This results in a further breakdown of the oxide/base layer interface of the tape. An effective
Figure 2-11.\A 100 feet of contaminated tape being removed from reel (stripping).
process to clean a tape is to use a magnetic tape cleaner/certifier similar to the one shown in figure 2-12.
Knives are used to remove any protrusions from the oxide surface. It is estimated that a maximum of 90% of all tape errors are removed in this manner.
Most tape cleaners clean tape by wiping the oxide and back surface of the tape. Loosened dirt, oxide particles, and other debris are removed from the tape by wiping assemblies. When the EOT marker is sensed by a photoelectric cell, the tape is automatically reversed, and the wiping assemblies clean the entire length of tape in the opposite direction. The wiping tissue used is made of a special textured fabric and is wound on a spool.
It is important to change the wiping material frequently at the point of contact with the tape. This is done to avoid entrapment and retention of abrasive dirt particles at the tape surface being wiped. Some tape cleaners, like the one shown in figure 2-12, move the wiping material along automatically.
In addition, most tape cleaners repack the tape as it rewinds, using a built-in machine programmed tension arm. This feature helps to relieve irregular tape pack tension, thereby reducing the possibility of tape deformation inside the tape reel. The repack tension arm is shown in figure 2-12.
Tape cleaning equipment that combines tape cleaning and recertification (figure 2-12) operates in the following manner. Any protrusions are removed by a knife edge during the first tape cleaning pass. At the same time, the location of every error that was not removed on the tape pass is indicated on a recording chart (figure 2-12, upper left-hand corner). The location of each error is identified by its distance from the beginning-of-tape (BOT) reflector. On the second pass, that is the return pass, the certifier stops at every unremoved error area and the operator, using a microscope, endeavors to remove the error with a sharp knife or scalpel. Upon completion, a recertification operation will usually restore the tape to a near error-free condition. On a 2,400-foot tape reel, each recertification operation averages 15 minutes.
All tapes\scratch tapes, work tapes, save tapes, and data tapes\should be cleaned after every 10 uses or every 90 days, whichever is more frequent. All tapes should have a cleaning label attached to the back surface of the tape reel. Each time a tape is cleaned, you should log the Julian date and initial the cleaning label.
Some helpful measurement criteria, used by several of the AIS installations for determining retention or disposal of magnetic tape, areas follows:
ABSOLUTE-END-OF-LIFE- The tape contains so many flaws (errors) that it can not function at all.
PRACTICAL-END-OF-LIFE- The tape can produce usable results, but because of cost and annoyance of failures, it is impractical to use it any longer.
LEVEL-OF-REJECTION- This is a judgment call and must be based on your past experience or expertise, you might say. Some librarians and management personnel feel that after a tape is cleaned, if 15 write errors occur throughout the tape, then the tape has reached the threshold of rejection.
Figure 2-12.\Tape cleaner/certifier.
TAPE-REPLACEMENT-LEVEL- This is the point at which the number of errors exceeds the rejection level.
Maintaining Magnetic Media
Maintaining media involves using specialized library equipment to clean, certify, and degauss magnetic media. It also involves seeing that media is in usable condition. The duties and responsibilities include the following:
Splicing leaders onto magnetic tapes
Placing BOT/EOT markers on magnetic tape
Rotating tapes and disks
Inspecting and changing disk pack filters
Setting up and operating tape cleaners, certifiers, and degaussers
Mounting and dismounting magnetic tapes
Performing cleaning, certifying, and degaussing functions
Performing emergency shut-down/power-off procedures on equipment
Setting Up, Operating, and Maintaining Equipment
Be sure you and the head librarian know and can explain the steps involved in setting up and operating equipment. Be able to demonstrate the proper way to clean, certify, and degauss magnetic media. Be sure all library personnel know how to properly perform emergency shut-down/power-off procedures on the different types of equipment used in the library (tape cleaner, certifier, degausser, and remote computer terminal, if used).
Like any area with equipment, some operator maintenance is required to assure proper functioning and also to increase the useful life of the equipment. Operator maintenance on tape cleaners and certifiers should be performed on a regular basis and include the following tasks: . Removing and replacing cleaning blades . Removing and replacing wiping tissues . Removing dirt/dust from photoelectric cells . Ensuring tape pack wheel is rotating freely
Ensure that proper and regular operator maintenance is performed on the library's equipment. Keeping a log of when it was conducted and when it should be done again will help. Make sure outer cabinets are kept clean and free of dust. All dirt, oxide particles, and other debris should be removed from the capstans, turrets, tape pack wheel, and cleaning blades. Cleaning blades should not be allowed to become nicked or dull. Also see that the wiping tissues are clean, and are rotating smoothly and automatically.