When Migrating a VTSS to Threshold (0) the DBU Does Not Drop to 0.0%

Asset ID:	1-72-1015009.1
Update Date:	2015-06-24
Keywords:

Solution Type Problem Resolution Sure

Solution 1015009.1 : When Migrating a VTSS to Threshold (0) the DBU Does Not Drop to 0.0%

Applies to:

Sun StorageTek VSM System - Version 4 and later
Sun StorageTek Virtual Tape Control Software (VTCS) - Version 6.2 and later
IBM z/OS on System z

Symptoms

When migrating a VTSS to Threshold (0), the DBU does not go down to 0.0%.
Attempting to migrate the VTSS buffer to zero but there is still DBU percentage with no VTVs remaining.
Trying to totally flush the VTSS of VTVs.

Cause

It is not unusual for the box to be unable to free up a small percentage of uncollected free space. The most important number to note is that there are 0 VTVs in the VTSS.

Solution

After the migrate to zero VTVs is initiated, VTCS will display the status of the VTSS using SLS6645I messages. These SLS6645I messages will display the DBU % and number of VTVs in the VTSS.

Once the VTSS has been completely drained of VTVs, the display will show a DBU % and 0 VTVs.

Example 1:  VTSS xxxx IS 45% FULL OF 0 VTVs

At this point, VTCS has migrated and subsequently deleted all of the necessary VTVs from the VTSS. It is not uncommon for the DBU to show a value other than 0%. The 45% as noted in example 1 above is called "uncollected free space". The VTSS will continue to convert this "uncollected free space" to "collected free space". This process may be time consuming; it could take minutes to over an hour to complete. Eventually the '% Full' value will drop to a number close to zero as noted in example 2 but usually, a small percentage of the DBU is not available to be reclaimed.

Example 2: VTSS xxxx IS 2% FULL OF 0 VTVS

Over time, this space that cannot be collected can build up and the only way to get the box back to 0% DBU is to have the field engineer run a clean on the box, which is performed when there are no VTVs in the buffer. Note that running a clean is not standard procedure. If the intent for draining the box is to run a clean on the VTSS, there is no need to wait for the uncollected free space number to drop before running the clean.

Examples 1 and 2 were taken from an actual customer site.

Once VTCS is reporting 0 VTVs left in the buffer, run the VTCS utility 'AUDIT VTSS(vtssname).
This will allow verification that there are no VTVs remaining to be migrated. Please make certain to use AUDIT VTSS and not AUDIT ALL. Instructions for running the VTCS AUDIT utility are in the VTCS Command and Utility Reference or the ELS Command, Control Statement and Utility Reference. To locate a current copy of the manuals, please review <Document 1014318.1>.

HINT: A manual IPT statesave could possibility speed up the collection process if having such a large number is of concern.

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