Can Datacom databases be allocated as Extended Format datasets?
Datacom database files for the index and data areas cannot be defined as SMS Extended Format or as a Sequential Extended Format. This means that they cannot be defined with the DSNTYPE=EXT SMS Data Class nor can they be defined with DSNTYPE=EXTREQ or DSNTYPE=EXTPREF or DSORG=PS-E in the JCL.
Furthermore, The DCB parms and sub parms should not be used for allocating a new dataset when using BDAM/EXCP for Datacom data or index areas. The DCB sub parms will be updated automatically once a DBUTLITY INIT is performed after initial allocation of the dataset.
As noted in the z/OS 2.2 version of the IBM DFSMS Using Data Sets manual (DGT3D410), Extended-Format Sequential Data Sets cannot be accessed using EXCP. Datacom uses EXCP processing for all database data and index areas (as well as the CXX, LXX and FXX), so these files cannot be defined as Extended-Format.
The reason for this exclusion is that extended format changes the internal structure of the data records, and the actual records will not match the DCB characteristics of the dataset. Also the internal structure of the blocks is changed slightly, so an EXCP-based program would not be able to read the dataset correctly.
For more information about IBM file types, please refer to the IBM manual z/OS DFSMS Using Data Sets (IBM manual SC23-6855-03).