Greg Saccomanno wrote:
I have checked the manuals and the archives on this and I am still unsure about mixing the yes and no values for SYNCHRES in a GRSPlex (Basic sysplex if that matters any). I need to bring my TEST LPAR into our plex for testing. I would rather wait until either our outage weekend next month to change the value of this on the systems that are already in the sysplex or until each cuts over to 1.7 but I need to bring the TEST system up in the plex and test before I can migrate 1.7 to the next system. I see that I can change the value via the SETGRS command and I guess I could always code the 1.7 system as SYNCRES=NO for this phase but from the way I interpret the FM it doesn't seem like it should be a concern. However, nothing I found gave a definitive answer. Does anyone know of any problems with having two z/OS 1.4 systems with SYNCHRES=NO and a z/OS 1.7 systems with SYNCHRES=YES active in a basic sysplex? Has anyone run this way when migrating to 1.7 from 1.4?
For decades, MVS has been using the SYNCHRES=NO technique. (Decades!) There was a "window of vulnerability" between the time the RESERVE macro was honored and when the RESERVE CCW was actually sent to the controller.This makes it possible, yet highly unlikely, that a RESERVE CCW sent from another system could be recognized by the controller during that "window" and the system now supposedly holding the RESERVE would be locked out. This problem scenario must be extremely rare. I've personally never seen it happen. Have you?
SYNCHRES=YES eliminates this decades-old issue. But, it's by no means required on any system. And, I can't imagine how mixing SYNCHRES techniques could create any new problems. The systems that specify SYNCHRES=NO will continue to have the same small exposure they've always had. The systems that specify SYNCHRES=YES won't.
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