Engine level mask
The Engine Level Mask (ELM) value determines which compression techniques are available for use by the VSAM data component and the non-VSAM data component.
BMC changes the ELM value when it introduces new compression engines and when it modifies existing compression engines. Not all modifications to existing compression engines require a change to the ELM value.
BMC provides a new ELM value when modifications to existing compression techniques require backward compatibility with the modified technique. For example, an older version of PACLOG may not be able to expand data that is compressed with the latest version of PACLOG.
The most current ELM value is set in the BCSS command sample named ALMELM. It is shipped with PACLOG as a member of the data set HLQ.V nnn.DBSAMP.
When you install a new release of PACLOG and change the ELM value, data that was compressed by the new engine may not be expandable by older engines. If you are testing the new release in a shared DASD environment, do not compress data that is accessible from multiple systems using new or enhanced engines unless these engines are available on all systems. Otherwise, expansion of the data on systems using the old engines may not be possible.
You can set an ELM value at the product level or the BCSS level. The product-level command (see Setting the PACLOG ELM) sets an ELM value that supersedes the BCSS value. BMC Software recommends that you set a product-level ELM value. The BCSS-level command (see Setting the PACLOG ELM) provides a default ELM for PACLOG and other BMC Software products that use BCSS but do not set a product-level ELM.