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Reorganization Selected system administrator activities
4. Physical volume inaccessible status
The PLM can no longer access the physical volume. This can be due to the following
reasons:
– The robot cannot access the physical volume.
– The tape header cannot be read.
The logical volumes affected may need to be read in again from a backup copy (dual
save) and backed up again.
4.4.2 How is a physical volume reorganized?
To prevent the reorganization process from overloading the system, the PLM always
reorganizes only one physical volume at a time. Once this physical volume has been
completely cleared (all logical volumes on the tape are invalid) to become a scratch tape,
the reorganization of the next physical volume can begin.
Since logical volumes cannot be copied directly from one tape to another, they are stored
temporarily in the TVC as follows:
1. The PLM selects a logical volume on the physical volume which is to be reorganized
and sends a “Move” request for each logical volume to the VLM.
2. The VLM checks whether this logical volume is located in the TVC. If it is, it sends a
“Restore” request to the PLM.
3. As soon as the TVC has a copy of the logical volume (again), the VLM sends a “Save”
request to the PLM. This causes the logical volume to be copied to another write tape.
From the point of view of the PLM, the logical volume has now been moved.
The PLM issues “Move” requests to the VLM for all valid logical volumes on a physical
volume in the ascending order of the block numbers on the tape. Once again, to prevent a
system overload, only a certain number of “Move” requests are initially sent. A further
“Move” request is not released until the preceding one has been completed successfully.