Calculating the size of storage and active control data sets

Before you allocate control data sets, you need to estimate their size. When calculating the size of either an ACDS or an SCDS, you have to account for system and base configuration information, SMS class, aggregate group, storage group, optical library and drive, and tape library definitions.

The following formula can help you determine the size of a source or active control data set:

size (bytes) = 150000 +
               (14000 * SG) +
               (2312 * (MC + SC + DC + AG + CS)) +
               (12000 * (DRV + LIB + VOL))

where:

150000 bytes

represent fixed data fields. For example, suppose you have the following configuration:

Five storage groups (includes copy pools)
Four management classes
Two storage classes
Five data classes
Two aggregate groups
6 optical libraries
24 optical drives
40 DASD volumes

With this configuration, the equation yields a value of 1088600 bytes for control data set allocation.

SG

is the estimated number of storage groups

MC

is the estimated number of management classes

SC

is the estimated number of storage classes

DC

is the estimated number of data classes

AG

is the estimated number of aggregate groups

CS

is the estimated number of cache sets in the base configuration (for record-level sharing (RLS) only)

DRV

is the estimated number of optical drives in the SMS complex to be managed by SMS

LIB

is the estimated number of optical and tape libraries in the SMS complex to be managed by SMS

VOL

is the estimated number of DASD volumes in the SMS complex to be managed by SMS

If you are running SMS in a Parallel Sysplex® environment with different releases of DFSMS, you must allocate your control data sets using calculations that are based on the highest DFSMS level. If you do not, your control data sets might be too small, because the storage requirements for classes and groups might be different between releases or new classes, groups, or other items might be added.

On a IBM® 3380 or 9345 DASD each track can contain 40 KB (40960 bytes). On a IBM 3390 DASD each track can contain 48 KB (49156 bytes).

If your SCDS or ACDS is not large enough, you might receive SMS reason code 6068 when attempting to save its contents. When reason code 6068 occurs, allocate a new, larger control data set and copy your existing SCDS into your new SCDS, or your existing ACDS into your new ACDS. You can then delete the old SCDS or ACDS and use the new one.

Allocating a new SCDS or ACDS resolves the problem only when reason code 6068 is caused by a data set size problem. Because this reason code is returned when a system service called by data-in-virtual (DIV) fails, the error might have other causes. Messages returned to you or the system console can help determine the cause of the failure.

Restriction: DIV has a current size limit of 4 GB. Make sure you do not exceed this limit.