When a mainframe host accesses a volume, the volume table of contents (VTOC) in the volume changes to include updated access logs.
Configuring the access attributes of a volume enables you to protect the volume from unauthorized writes and reads. Do not configure the access attributes of a volume while jobs handling data on the volume are running. The running jobs might end abnormally.
When setting the size of the VTOC area, the following conditions must be met:
- The access attribute of the volume is Read Only.
- The storage system model name is type A (A-65AF-CBXA).
The storage system with model name type H (H-65AF-CBXA) does not support setting the VTOC area size.
- The volume is not for VM minidisk use.
- The VTOC location is not modified by using the VTOC parameter for the ICKDSF INIT command on the volume.
Do not assign the read-only attribute to a volume whose VTOC location has been changed by using the VTOC parameters of the ICKDSF INIT command. If you assign the read-only attribute to a volume whose VTOC location has been changed by the VTOC parameters, the host might not be able to write the access logs in the VTOC, as shown in Example 1. The host tries to write updated access logs in the VTOC whose location has been changed, however the host cannot write due to the read-only attribute.
Example 1: The read-only attribute is assigned to a volume whose VTOC location has been changed by the VTOC parameters of the ICKDSF INIT command.
If you configure the VTOC area size settings for a volume with the read-only attribute by using Volume Retention Manager, the dataset can be updated and the read-only attribute might not be applied, as shown in Example 2 below.
Both of the following settings are configured:
- The read-only attribute is assigned to a volume whose VTOC location has been changed by using Volume Retention Manager.
- The range up to the VTOC whose location has been changed is set for the VTOC area for Volume Retention Manager.
The user dataset A is located in the VTOC area that was set by using Volume Retention Manager. The read-only attribute cannot be applied because the host can write updates.
Example 2: