Setting the IAM Global options

The next step is to review and make whatever changes are necessary to the IAM Global options. Many of the various default values for IAM can be changed in the IAM Global options table. For example, defaults for buffers, Data Compression, SMF recording and many others can be changed using this capability. The defaults are changed by executing the IAMZAPOP utility program. The use of this program and all of the default values and options are fully described in IAM-Global-Option-Change-Facility of the IAM User Manual. This section will discuss what is new and changed in this version, how to use the IAM Global options change capability along with some examples, plus make some recommendations for changing some of the defaults.

Users of prior versions of IAM

The first step in determining what Global options should be changed is to find out the previously changed Global options. Users of prior versions can determine what Global options they have changed in their current release through the use of the IAMZAPOP AUDIT function. This is a critical part of installing a new release or level of IAM to ensure that existing applications will continue to run as they have with prior levels. Below is an example of running the AUDIT function.

Example of IAMZAPOP AUDIT command

JCL to run AUDIT Function of IAMZAPOP (EX9004A)

AUDIT command output

An example of the output from the AUDIT command follows. Note that it prints the name of the load library. The changed Global Option(s) keywords are displayed, followed by the current value, and the default value. From this example, we see that the following Global options were changed:

• RECTYPE=201
• SMF=YES

These options are important to maintain across releases, as they provide for IAM SMF data to be collected, and enable customers to obtain reports on IAM activity using the IAMSMF or IAMSMFVS programs, or their own programs.

Also, you can obtain this AUDIT report through the IAM ISPF panels.      

Example of output from AUDIT command

Recommended Global option changes

The next step, after determining what Global options had been changed for the prior version, is to review the various default values and determine which, if any, would provide a benefit to your installation. IAM-Global-Option-Change-Facility of the IAM User space describes the various options available. We recommend that you consider changing the following Global Option values from their default settings.

• Set ESDSINTEGRATED=5 or higher to allow for updates to ESDS files to remain in their original block. While VSAM (and IAM) do not allow a record length to change on update processing for ESDS files, the record lengths can change due to data compression. It is better for overall performance to minimize the use of overflow, as much as possible which is accomplished by defaulting to providing some integrated overflow for updated ESDS files.
• Set SMF=YES and RECTYPE=201 to enable the IAM SMF records. This will provide a way, through SMF reports, to monitor and track IAM data set usage. With this option enabled, the IAMINFO reports will be available from the IAM SMF records. This may prevent rerunning jobs just to obtain an IAMINFO report, should one be necessary. Valid record types are from 128 to 255. Make sure to select a record type that is not being produced by other software packages.

There are also a few options that you may have to set for compatibility with other software products. In particular, the following options may have to be set as indicated:

• Set DYNCAT=YES if you are using the BMC MAINVIEW product.
• Set ENABLE=BIM if you have any of the VSAM products from B. I. Moyle.
• Set ENABLE=VAM if you have CA-ALLOCATE.
• Set ENABLE=SAFRC4 if you are using a product other than RACF for security, such as ACF2 or Top Secret to make sure that security decisions are being when opening data sets.
• Leave DSORG=PS set, particularly if you use DFSMSdss or DFSMShsm to backup your data sets. If IAM files have a DSORG of DA set, these products may not be able to restore IAM data sets, particularly if they are multi-volume.

Other Global option considerations

There are a few other Global options that should also be considered, which may need to be set depending on your installation requirements. These include the following:

• While rather rare, there are some applications that require the setting of the Global Option ENABLE=NOREUSE for proper function. Such applications require an open error to occur when opening a non-reusable VSAM data set to prevent overlaying a previously loaded file. By setting this Global Option, IAM will follow VSAM rules for reloading data sets without a Delete and Define as based on the Define parameters.
• If you already have CICS regions of 512 MB or higher, then consider raising the default value for MAXREGION to allow IAM to increase the region of those CICS systems if necessary. With a default value of 512 MB, IAM will not be able to increase the region for CICS systems that already have the large region value.
• If X37 abends have been a problem, consider revising the MAXSECONDARY default values. This facility acts as a multiplier that IAM will use when requesting another extent. Because IAM files that are not DFSMS Extended Format are limited to 16 extents per volume, use of this facility will increase the amount of DASD space requested without having to change the IDCAMS DEFINE. This option is not used for IAM files that are in the DFSMS Extended Format.
• Consider how you prefer allocations to work for multi-volume data sets. Depending on this option, IAM will request either the primary or secondary space when it appears that a volume switch will occur. The keyword is MULTIVOLUME=[ PRIMARY | SECONDARY]. Because IAM does not have control over whether or not a volume switch occurs, this may not always work as desired, particularly when the primary space value is less than the secondary. This option is not used for IAM files that are in the DFSMS Extended Format.
• If you have a DFSMS STORCLAS that causes data sets to not be SMS managed, such as NONSMS, then set the IAM Global Option STORCLAS to that value.

Setting IAM Global options

Once you have decided on the Global options you want to change, use the program IAMZAPOP to change them. Global options can also be changed subsequent to the product installation as may be needed. The following JCL and control card example demonstrates how to set the recommended Global Option values. For complete information on setting and changing the IAM Global options Table, see IAM Global Option Change Facility.

Example of setting Recommended Global Option Values (EX9004B)

The above example also includes a PRINT command. This will print out the Global Option settings, and can be done whenever a list is necessary. It is a good idea to review this listing, to make sure that the Global options are set as you expect them to be. The PRINT command does not need to be preceded by the ZAP command, so a listing of your Global options can be obtained whenever necessary.

You can also change the IAM Global options through the IAM ISPF panels as displayed in the following ZAP command: