Working with virtual tapes

A virtual tape cannot be relocated, i.e. the attributes HOME-LOCATION, FREE-LOCATION and TEMP-LOCATION must all be the same. Any actions causing a relocation are rejected by MAREN and MARENADM.

A virtual tape cannot be exported: the EXPORT-VOLUME statement is rejected with the message MARM015 if the current location (TEMP-LOCATION) and the ROBAR-2 operating mode are defined.

The RETURN-VOLUME statement is not executed for a virtual tape because the current location (TEMP-LOCATION) and the home location (HOME-LOCATION) must always be the same.

Changing the location

The location of a virtual tape (and of other tapes, too) can be changed using the MODIFY-VOLUME-ATTRIBUTES statement. To do this, the HOME-LOCATION, FREE-LOCATION and TEMPORARY-LOCATION operands must be modified to indicate the same location. This new location must offer the operating mode ROBAR-2 (ETERNUS CS). Parallel to the location being changed in MAREN, corresponding modifications must be made in ETERNUS CS.

Support of the fast mount attribute

After a virtual tape has been defined in ETERNUS CS or after it has been initialized, it is implicitly given the “fast mount” attribute. “Fast mount” means that the tape is immediately available for processing and time parameters such as mounting, etc., are not required for “fast mount” tapes. If user data is written to the tape, ETERNUS CS will make sure that it is saved on a real tape. Once this has been done, the reserved cache area can be released and another virtual tape can be used. The tape is no longer a “fast mount” tape once its data has been overwritten in the cache.

The “fast mount” attribute only describes a virtual tape’s status in ETERNUS CS. It cannot be assigned as a tape attribute in the MAREN catalog.

When MAREN or ROBAR determines that the next access to a virtual tape can only be a write operation from the beginning of the tape, they cause ETERNUS CS to assign the “fast mount” attribute to the tape. This happens in the following situations:

• The virtual tape was initialized either using the MARENADM statement INIT-VOLUMES or the INIT utility routine. Since ROBAR recognizes whether a virtual tape is initialized or not, it causes the attribute to be modified.
• The virtual tape was released using the MARENADM statement FREE-VOLUMES. MAREN causes the attribute to be modified, i.e. MAREN sends console message MARM1S1 to ROBAR. The message requests a confirmation of whether the attribute modification has taken place. If the answer is negative, MAREN cancels the FREE-VOLUMES statement. If the statement included a list of VSNs, the cancellation applies to all the volumes in the statement. The release will have to be repeated for the VSNs that are not affected.

Differences in the release of virtual tapes and real tapes

• A console message that requires a response is sent to ROBAR for each virtual tape that is to be released. Therefore releasing virtual tapes may take somewhat longer than releasing real tapes.
• The data on a virtual tape cannot be recovered following the release of the tape with FREE-VOLUMES. In the case of a real tape, the data will not be lost until the tape is reinitialized or overwritten.
• If a virtual tape is not initialized, the next access must be a write operation at the beginning of the tape. Otherwise the tape will not be consistent and system errors may occur. For that reason, the catalog entry for virtual tapes should contain INIT=YES.