Unless set up otherwise, the ICL grows continuously over time as more certificates are issued. The size of a certificate varies depending on many factors; for example, the public key type and size, the length of the issuer and subject names, the number and size of Subject Alternative names, and the number and size of certificate extensions. Assume an average size of 1024 bytes of storage for each ICL record. With an allocation of CYL(3,1), the data set can have a maximum of 125 cylinders on a single 3390 volume for a total size of 105 MB. This would mean the data set should be able to hold at least 102,500 certificates. If multiple volume support is used, you can double this amount.

If your anticipated needs differ greatly from the above value, you need to adjust the space allocation parameters CYL(3,1) on the DEFINE CLUSTER statement for the ICL. (This is the second DEFINE CLUSTER statement in IKYCVSAM. See IKYCVSAM for a code sample of this file.) You might also want to proportionally adjust the space allocation parameters TRK(5,1) on the DEFINE ALTERNATEINDEX statements for the ICL. These are defined in the DEFALTDX job step. (Their names contain the icl qualifier.)