Cache Management › Determining the Global VCAT and BSDS Size

Determining the Global VCAT and BSDS Size

The Global VCAT and BSDS1 are the same size and should be allocated on separate DASD volumes to ensure recoverability. The size of the data sets is based on a fixed area of 7,298 records for control information and one 4KB record for each Virtual VOLSER that needs to be indexed. The following algorithms can be used to determine the size of the Global VCAT and BSDS1:

Control Information Area + VOLSER Area = Total Size

7,298 records + Total VOLSERs = Total Records

608 3390 tracks + (Total VOLSERs / 12) = Total 3390 Tracks

For example, if your Global VCAT will contain 100,000 VOLSERs, the total number of records used in the IDCAMS DEFINE statements and the resulting size of the Global VCAT and BSDS1 would be:

7,298 + 100,000 = 107,298 records

608 3390-tracks + (100,000 / 12 ) = 8,942 3390-tracks

The JCL to define and initialize the Global VCAT and BSDS will be generated by the Customization Panels later in this chapter. This algorithm is provided to allow you to pick DASD volumes with enough available space to prevent allocation errors.

The Customization Panels will default to indexing 1000 Virtual VOLSERs which is adequate for a trial or demonstration installation. For a live or production installation, a minimum of 100,000 VOLSERs is recommended since the Global VCAT and BSDS cannot be dynamically extended. All Subsystems using a specific Global VCAT and BSDS1 pair must be stopped so these data sets can be reallocated and repopulated.