Write Once, Read Many (WORM)

The write-once, read-many (WORM) function of tape data storage is accomplished on the 3592 Model E05 by a combination of microcode controls in the drive, and a special WORM tape cartridge (MEDIA6, MEDIA8 or MEDIA10). All 3592 drives are capable of reading and writing WORM cartridges.

When the drive senses that a cartridge is a WORM cartridge, the microcode prohibits the changing or altering of user data already written on the tape. The microcode keeps track of the last appendable point on the tape by means of an overwrite-protection pointer stored in the cartridge memory (CM). Statistical Analysis and Reporting System (SARS) data can be written and updated on WORM tapes because the SARS data is not in the user area of the tape. Each WORM cartridge is identified using a world-wide unique cartridge identifier (WWCID), which is permanent and locked, providing another level of security for data that must be maintained. This permanent locked information is stored in both the cartridge CM and on the tape itself, and can also be associated with the unique barcode VOLSER.

Note: In some publications, the world-wide unique cartridge identifier (WWCID) may also be referred to as the world-wide identifier (WWID).

While overwriting of data on a WORM cartridge is not allowed, appending is permitted under certain conditions. These operations are allowed:

Appending an additional labeled file following the final file on a tape volume. This overwrites the final tape mark of a final pair of tape marks followed by a header label group for the file to be appended. Appending is only permitted where the trailer label group begins with a record that starts with EOF rather than EOV. EOV indicates that a file has been extended to a different volume.
Appending an additional unlabeled file following the final file on a tape volume. This overwrites the final tape mark of a final pair of tape marks followed by the user file to be appended.
Appending additional records to the final labeled file on a tape volume. This overwrites the final trailer label group and the tape mark immediately prior to the final trailer label group followed by the final file's user data records. Appending is only permitted where the trailer label group begins with a record that starts with EOF rather than EOV.
Appending additional records to the final unlabeled file on a tape volume. This overwrites the final tape mark or pair of tape marks immediately following the last user data record of the unlabeled file.
Relabeling a tape volume when only a header label group has been written and no user data records nor trailer label group has been written. This rewrites the header label group, including volume labels and remaining initial header label group records, where volume identification and other fields in the header label group may be changed. This is prohibited if the header label group was followed by a trailer label group, user data records, or more than two tape marks because user data is never overwritten.
Header label groups and trailer label groups are recognized when all records within them conform to either IBM Standard or ANSI Standard label definitions. Any record with a prefix not recognized as conforming to these standards is assumed to be a user data record and causes overwriting of the entire label group to be prohibited. Double tape marks are assumed to occur only after the final recorded unlabeled file or the final label group on a tape. More than two adjacent tape marks indicate a null structure, such as a null user data file, between the first two of the multiple adjacent tape marks. For this reason, no more than two final tape marks are overwritten in any attempt to append.

In addition, the 3592 drive permits certain normal error recovery actions to succeed when writing to a volume that had been previously interrupted due to some equipment, connectivity, or power malfunction. In particular, in ESCON and FICON attachment environments, certain channel error recovery programs are supported via a mode of operation where the ESCON or FICON controller simulates the rewriting of records. The simulation of rewriting of records presents the appearance at the host of successful rewrites of logical records. The simulation succeeds only if the actual record already recorded on the medium precisely matches the record sent to the 3592 drive from the host.