the virtual volume selected by the library manager to satisfy the request. No recall of the data from the previous usage of the volume is performed because the fragment contains the label information needed by the host tape management software to validate the use of the volume for a non-speci®c mount request. The subsystem signals the host that the mount is complete when the fragment is accessed. The result is a very short mount response time because no physical movement or mounting of a cartridge is involved.

If a mount request speci®es a category that has not been de®ned as ªFast Readyº, the library has no indication that the application intends to write from the beginning

of the volume. It is likely that the selected virtual volume will not be resident in the tape volume cache and will have to be recalled from physical tape.

Deletion of VTS Logical Volume

Logical volumes in a VTS can only be deleted under the control of the attached hosts. A logical volume can be deleted only if it is in the Insert category or a category with a Fast-Ready attribute set (see ªSet VTS Category Attributesº on page 166). When a logical volume is deleted, it is removed from the library's inventory and any data that was associated with the volume is deleted. A logical volume which is in a Fast-Ready category is deleted from a VTS by performing the following steps. (A logical volume which is in the Insert category is deleted from a VTS by performing step 2 only).

1. Assigning the logical volume to a category within the library that has the Fast-Ready attribute assigned. This is accomplished by the tape management system when the data associated with the volume reaches its expiration date and the volume is returned to the scratch pool.

2. Subsequently, assigning the logical volume to an eject category. This can be

 

done by asking that the volume be ejected from the library, using

 

platform-speci®c library control interfaces; for example, with MVSE/ESA or

 

OS/390, through the tape management interfaces, ISMF panels or MVS

 

operator commands.

 

Note: Once a logical volume has been deleted from the library, data on the volume

 

is deleted and cannot be recovered.

Scratch Stacked Volumes

It is essential that sufficient scratch stacked volumes be available for use by a VTS

for copying a virtual volume when the volume is closed. A warning is provided when

the Free Storage Threshold cannot be met with the scratch stacked volumes which

are available. See the Set VTS Management Policies Pop-Up Window, shown in

Figure 99 on page 169. The number of empty scratch volumes can be determined

by using the Search Database for Volumes pop-up window, Figure 83 on page 140,

with a Search Criteria of category FF03. The records found will be the count of

empty scratch volumes.

The Reclaim Threshold Percentage as entered on the Set VTS Management

Policies pop-up window becomes important when the supply of scratch stacked

volumes is low. The VTS Space Reclamation Algorithm may impact the VTS

performance when it is necessary to reclaim expired space on stacked volumes. A

high Reclaim Threshold Percentage requires that more active data be moved (using

VTS resources) to free the stacked volume for scratch use. As a general rule, you

should try not to go above 30% to 40% as a Reclaim Threshold Percentage. It is

better to add additional stacked volumes rather than raise this value. When there

Chapter 3. Operational Characteristics 43

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IBM Magstar 3494 manual Deletion of VTS Logical Volume, Scratch Stacked Volumes