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Managing Media in Networked Environments
Michael Kramer
B&L Associates, Inc.
220 Reservoir Street, Ste. 15
Needham, MA 02494 USA
(781) 444-1404/5805 fax
mkramer@bandl.com
MAINFRAME OPERATING SYSTEM LOGGING
Legacy systems operate in a defined environment controlling a limited set of media. This is even demonstrated in the terminology. In open systems the term media management is used to recognize the wide range of tape, DAT, CD and other media which must be managed. In legacy systems, it is primarily tapes that are managed, so the terms tape library system and tape management system are in common usage.
In legacy systems, when a new tape is mounted into a mainframe drive, a label is created on the tape by the operating system. The initial internal label on a new tape may only consist of the tape's serial number, which matches the outside serial number. When data is written to tape, the "tape header information" will contain the serial number, the volume name (data set name), when the tape was created, the block size, and other information more specific to the particular operating system. When a tape is mounted, an operator at a supervisory console can see all of the attributes of the tape as well as the drive unit in which the tape is mounted.
Once the tape is mounted into the drive, the tape can be read from, known as opening a tape for input, or it can be written to, known as opening a tape for output. In a process called automatic purge protection, a logging request goes directly to the operating system before a tape is opened for output from an application. The operating system then queries the tape library system to determine if there is a "scratch" tape mounted that can accept the application's data. The tape management system examines the internal labels of the mounted tapes. If a tape is available to be written to, the tape management system will inform the operating system that the tape in the specified tape drive is available to be purged, and have new data written to it.
For example, a payroll application has written data to a tape and has called the volume "payroll files." The operating system queries the tape management system for a tape that can accept payroll files. The tape management system examines the tapes in the drives and compares them to the tape information in its database. If the database shows that none of the tapes have passed their retention period (i.e., the data on the tapes have not yet expired), it will report to the operating system that no tapes are available. The operator must then mount another tape that can accept the data and rerun the automatic purge protection process. This ensures that the data is always retained for the defined period without a user rewriting over the tape. If the tape management system looks in its database and finds that there is a "scratch" tape in the drive, which means it is available for reuse, the tape management system will authorize the operating system to purge the specified tape in the specified drive.
When the tape is opened for output, the tape label information is written first and includes the volume identification of "payroll files" and the other attributes described above. The tape management system, which has a hook into the operating system, accesses the information through the operating system logs. It then records the information into its database. Based on predefined parameters for "payroll files" in the tape management system database, the tape management system knows how long a piece of media with "payroll files" on it needs to be retained and when it should be moved.
