Configuring Your Product › Customization Options › The CA Disk SVC

The CA Disk SVC

CA Disk SVC updates a data set VTOC entry, recording the last used date, for example. The SVC has the following advantage over the IBM SU 60 update code: exemption entries are provided such that the product management tasks themselves do not cause data sets to appear used.

Zaps to one or more IBM modules must be applied to call the CA Disk SVC to do the updating.

The CA Disk SVC maintains the SU 60 change bit and last used date fields. SVC also maintains extra CA Disk defined fields and provides the facilities to overcome the SU 60 deficiencies.

The two fields that IBM SU 60 maintains appear to provide the information that you need to help manage disk storage. CA Disk functions can examine the two fields and can execute without the CA Disk SVC being installed. The SVC is required for your implementation for the following reasons:

• The CA Disk storage management tasks open user data sets to perform the management functions, such as, backup, migration, and compression. IBM SU 60 open hook marks these data sets as being used whenever the management functions are run. The IBM SU 60 prevents other functions, such as archive, from finding and processing data sets that are truly inactive. A potentially large number of data sets appear used and are kept on disk because of storage management jobs routinely being run. The CA Disk SVC exempts the management jobs from causing these updates.
• The CA Disk SVC can also record the date whenever the change bit is turned on (mod date). This record is useful in report information. SVC also provides a convenient and low-overhead means of eliminating redundant backup copies of data sets (that full pack dumps or other techniques often create). For more information about recording the date, see "Backup and Archive Consideration" in the User Guide.
• The CA Disk data set utilization (DSU) report loses much of its usefulness because it reports on the additional fields that CA Disk SVC maintains.

Note: HFS data sets, DB2, and certain other applications bypass normal open processing and do not maintain a last modification date.

SVC Requirements

If you are going to install CA Disk SVC, provide a user SVC of type 3 or 4. Enable the SVC for interrupts and designate as either restricted or nonrestricted.

Note: For more information, see User SVC.

SVC Integrity and Security

Before any fields are modified in the DSCB, the SVC verifies that all INPUT parameters contain an F1-DSCB. SVC also checks to ensure that the caller is in key 0 and in supervisor state.

VTOC Fields Maintained by the CA Disk SVC

If the IBM modules are zapped to execute the CA Disk SVC, the following fields are maintained in the F1-DSCB for each data set:

1

Last use date.

Format: ydd

Bytes: 3

Offset (DEC): 75 SU 60

2

Last modify date.

Format: ydd

Bytes: 3

Offset (DEC): 70

3

Job name or account code.

Format: char

Bytes: 8

Offset (DEC): 62

4

Count of updates to VTOC entry.

Format: bin

Bytes: 2

Offset (DEC): 73

E5

Change bit.

Format: bit

Bytes: x'02'

Offset (DEC): 93 SU 60

6

SVC mode.

Format: char

Bytes: 1

Offset (DEC): 103

Optionally, you can specify Fields 1 and 2 as a 4 byte packed format (ccyydddF). If they are specified, adjust some of the field offsets to prevent overlaying other format 1 DSCB fields. The macro settings within the CA Disk SVC determine Field 3. You can elect to maintain an accounting code or job name. The accounting code measures from the first accounting field on the JOB statement for the job or user accessing the data set. You can also select how to maintain this field:

• The first time the data set is updated.
• Each time the data set is modified.
• Each time the data set is used.