When upgrading to z/OS V2R4, you might notice an unintended value for DDRSIZELIM parameter displayed by issuing a new DISPLAY DEVSUP command.
z/OS V2R4 introduced a new DISPLAY DEVSUP command to display the system settings that have been set by DEVSUPxx members of the logical parmlib. That's great!!!
The suffix for DEVSUPxx parmlib member can be specified by DEVSUP=xx parameter in IEASYSxx, and if DEVSUP=xx parameter is omitted, we get a following command response.
D IPLINFO,DEVSUP
SYSTEM PARAMETER 'DEVSUP': NOT_SPECIFIED
In such case, DISPLAY DEVSUP command shows "DDRSIZELIM=0M" in output message IEA253I which means "no limit" while the manual describes as follows.
z/OS Version 2 Release 4
MVS Initialization and Tuning Reference (SA23-1380-40)
Chapter 28. DEVSUPxx (device support options)
DDRSIZELIM={xxxx|xxxxM|1000M}
DDRSIZELIM=
Specifies the limit on storage usage for Tape DDR swap.
<snipped>
The default value for this parameter is 1000 megabytes.
So, is it a correct behavior to show "DDRSIZELIM=0M" in this case?
The answer is Yes. "DDRSIZELIM" default is only set if DEVSUPxx parmlib member is found and the parameter is not specified.
DOC APAR OA59272 (June 2020) has been taken to clearly state the default behavior in the DDRSIZELIM explanation.
| The default value for this parameter is 1000 megabytes if there is a DEVSUPxx parmlib member found and
| either DDRSIZELIM is not specified or it is specified with no value.
| If there is no DEVSUPxx parmlib member found at IPL time, DDRSIZELIM will be set to 0 MB.
After the system initialization is completed, if we activate a new DEVSUPxx parmlib member via SET DEVSUP=xx command which does not specify the "DDRSIZELIM" parameter, "DDRSIZELIM=1000M" is correctly set by default.
Hope it helps you.
Thanks!