Pete Clark on z/VSE: Virtual Storage Constraint Relief: Courtesy of VSE/VTAM
by Pete Clark
May 1, 2006
** Read this article online at http://www.mainframezone.com/operating-systems/pete-clark-on-zvse-virtual-storage-constraint-relief-courtesy-of-vsevtam
What would the average VSE systems programmer do to get 50K to 500K of free 24-bit system GETVIS (Get Virtual Storage)? Would you consider doing a little system maintenance work? I sure would.Many z/VSE systems programmers may know of a time when they literally would have committed some heinous act to free up any 24-bit system GETVIS.In the current VTAM implementation, only XDBUF (exchange identification buffers) and IOBUF (input output buffers) still use 24-bit storage if 31-bit storage is available. XDBUF uses 24-bit partition storage and is reasonably small with few buffers required, and therefore presents no problem. IOBUF uses 24-bit system GETVIS, a critical storage resource actively managed in many z/VSE installations and for some sites always in short supply.Well, the latest enhancement to the z/VSE system is available via PTF (Program Fix) and offers significant VSCR in 24-bit system GETVIS: You can order or download PTFs VSE/VTAM - APAR DY46471, PTF UD52964 and z/VSE - APAR DY46396, PTF UD52873 (AF Base) or UD52874 (Generation Feature).Installation of these two PTFs to a z/VSE system will enable 31-bit GETVIS support for IOBUFs by VSE/VTAM. Both PTFs are required for 31-bit IOBUF implementation; failure to install both means no 31-bit IOBUF support and error messages if you try to implement it.After installing the PTFs and doing an IPL to activate the support, add the VTAM parameter in Figure 1 to the VTAM start-up member. If you specified the YES option, 24-bit IOBUF storage is acquired from 31-bit storage.
Note: IOBUF31=YES and VTAM support of any Integrated Communications Adapter- (ICA-) attached devices (e.g., SDLC, BSC, X.25 and LAN) are mutually exclusive; i.e., when YES is specified, ICA resources can’t be activated.For z/VSE users who utilize the default as installed environment, the 10K to 100K savings of 24-bit system GETVIS may not be that dramatic. However, even 10K can be very important when needed.For z/VSE users with numerous active terminal and printer VTAM sessions, savings in excess of 500K-plus of 24-bit system GETVIS aren’t unusual. For z/VSE users with large active VTAM networks, this is a major VSCR enhancement and well worth the few minutes required to install the support, IPL, and change the VTAM start-up member.A new console display command is available to confirm the implementation. Simply enter the following command on the VSE console:D NET,VTAMOPTS,OPT=IOBUF31 The z/VSE folks have published an informative document on the z/VSE Website about this new enhancement. You can download the document “z/VSE VTAM 31-bit I/O Buffer Support” from HTTP://www03.ibm.com/servers/eserver/zseries/zvse/news/.VSE 2.7 and Earlier For VSE users on VSE 2.7 and earlier, the VSE PTF isn’t applicable, but the VTAM release is the same, so the VTAM PTF can be installed. However, since both PTFs must be installed to activate the support, those users can’t put IOBUFs in 31-bit storage.Gaining 50K to 500K of system GETVIS is another good justification for installing z/VSE 3.1.1, rather than remaining on an earlier release.Conclusion The installation is easy and the implementation even easier—two PTFs, one IPL, and one parameter addition.Many VSE users will regain much-needed 24-bit system GETVIS that will be used for new facilities and to improve performance and stability.The 31-bit IOBUF support has been a WAVV requirement and a user request. We can now mark those as accepted/delivered, and say thanks to everyone for listening to the customer.Thanks for reading the column; see you all in the next issue.
