SECONDARY CYLS on CXX Report

Products

• Datacom
• Datacom/DB
• DATACOM - AD
• Datacom/AD

Issue/Introduction

On a full CXX Report, in the Area section, where does the SECONDARY CYLS value come from and how can it be changed?  

AREA NAME  - AAA
.
.
TOTAL TRACKS  -   184,710          DYNAMIC EXTEND -    YES
PERCENT FULL  -        68          DYN.EXT.CYLS   -  1,500
DEVICE TYPE  - 3390                SECONDARY CYLS -      20                 

Environment

Release: 15.1

Resolution

Documentation section Directory (CXX) Reports explains the SECONDARY CYLS value.
It is the secondary allocation specified in the SPACE parameter in the JCL when the file was first allocated - SPACE=(CYL,(50,20).
This information comes from the VTOC entry for the file in the format 1 DSCB.
It is reported by Datacom but cannot be changed from within Datacom and there's no easy way to change it in z/OS without a utility that can edit the VTOC information. 

In any case there is no need to change it as a Datacom dynamic extend will use the value specified in DYN-EXT-TRACKS for the secondary extent allocation.

Only if DYN-EXT-TRACKS is 0 will it try to use the secondary allocation value in the VTOC or if the file is allocated to the MUF with a DD statement in the JCL which specifies a secondary allocation, then we'll use that instead of the one in the VTOC. However most sites would not have DD statements for Datacom files in the JCL and would not normally specify secondary extents.

You can also specify the size of the secondary extent allocation in the DYNAMIC_EXTEND console command - DYNAMIC_EXTEND nnn,aaa,200,CYL

The size of the extent allocation used by Datacom dynamic extend is documented in section Creating and Maintaining Data Areas 

In a z/OS environment:

• If DYNAMIC-EXTEND=Y and DYN-EXT-TRACKS= is not zero, the dynamic extend occurs using the DYN-EXT-TRACKS= value.
  
  
• If DYNAMIC-EXTEND=Y and DYN-EXT-TRACKS=0, MUF uses the amount of the secondary extent of the data set as specified in a DD statement in the MUF startup JCL (if specified with a secondary allocation), or else MUF uses the DSCB of the VTOC (if it provides a secondary allocation). Secondary allocation, however, is always used after an area is opened. But if a directed (console-like) DYNAMIC_EXTEND is done and selects an override value for the number of tracks/cylinders, this override remains and is used for any normal dynamic extends, until the area is closed and reopened.

 

Additional Information

See article 45305 - Enabling Dynamic Extend for Datacom areas