Configuring Your Product › Customization Options › The CA Disk SVC › CA Disk SVC Modes

CA Disk SVC Modes

The CA Disk SVC is distributed with a control switch called SVCMODE that affects which fields are maintained and how often.

SVCMODE=4

This mode of operation makes the minimum number of updates to the VTOC entry (F1-DSCB) for a data set, yet maintains all of the fields. The SVC source is distributed in this mode. It updates the F1-DSCB only if:

• The last used date needs to be changed.
• The change bit needs to be set on (change bit turned on when data set opened for output), and MODDT is also updated

Note: (1) causes only one update per day, and (2) causes only one per day unless the change bit is being turned off more often than that (for example, running incremental backup two or more times per day).

Field 4 shows the number of times the F1-DSCB has been updated, not necessarily the number of times a data set has been opened.

SVCMODE=5

This mode of operation causes updates under exactly the same conditions as mode 4, but only the SU 60 fields (1 and 5) and the mode field itself (6) is maintained. This is an SU 60 look-alike mode, with the benefit of the exemption tables.

SVCMODE=6

This mode of operation causes the F1-DSCB to be updated every time the data set is opened. Field 4 shows the number of times the data set has been opened.

This technique causes many more updates of the VTOC entry, and is known to cause occasional problems with partitioned data sets, made evident by duplicate TTR directory entries and loss (overlay) of a member update. This usually occurs only for PDSs that are accessed very heavily and by two or more concurrent users. Shared DASD environments without a cross-system enqueue package are especially susceptible.