PAGE

PAGE={dsname|*NONE*                   }
     {(dsname1|*NONE*)[,dsname2|*NONE*,[dsname3,...[,L])}
     {(,L)                     }

This parameter allows the installation to name page data sets as additions to existing page data sets. The maximum number of page data sets is 256. The system determines which page data sets to use by merging information from three sources: IEASYS00, IEASYSxx, and the PAGE parameter.

During system initialization, the system first uses the list of page data sets specified on the PAGE parameter of the IEASYS00 parmlib member. It then uses any other IEASYSxx parmlib member (identified via the SYSP=xx parameter). The IEASYSxx PAGE data set name list overrides the one in IEASYS00.

PAGE=dsname and PAGE=(dsname1,dsname2,...[,L]) allow the operator to add page data sets to the list of data sets already specified in IEASYSxx. If the PAGE data set name list in IEASYSxx is null, the operator specification is used.

The system generates a list of all the page data sets that the initialization routines have opened. If the L keyword is specified (either in parmlib or from the operator's console) this list is, then written to the operator's console and to syslog. If the L keyword is not specified, the list is written only to the syslog.

The system interprets the final merged sequence of page data set names that are specified as follows:

The first named data set on the list is used as the PLPA page data set. This data set contains pageable link pack area (PLPA) pages. If *NONE* is specified, no PLPA page data set is used and no quick or warm starts can be performed. *NONE* can only be used when Storage Class Memory (SCM) is online and used for paging (refer to PAGESCM).
The second named data set in the list is used as the common page data set. This data set contains all of the common area pages that are not PLPA pages. If *NONE* is specified, no common area page data set is used. *NONE* can only be used when Storage Class Memory (SCM) is online and used for paging (refer to PAGESCM).
The third and all subsequently named data sets are used as local page data sets. These data sets contain all the system pages (including VIO pages) that are considered neither PLPA nor common data set pages.

Note: To replace local page data sets during an IPL, you must specify the CVIO parameter. (Note that CLPA implies CVIO.)

If Storage Class Memory (SCM) is online and used for paging (refer to PAGESCM), SCM will be used for all page types, in addition to the page data sets specified by the PAGE= parameter.

When defining page data sets, you must ensure that the desired PLPA page data set is the first entry in the data set list, in both IEASYS00 and IEASYSxx.

During initialization, there are no checks on the sizes of user-supplied data sets. When initialization completes, the PAGEADD command can be used to add more local page data sets to the system. The most current page data set information is preserved so that it can be used for subsequent quick start and warm start IPLs.

The data set intended for PLPA should contain enough space for the entire PLPA, including the extended PLPA. If the entire PLPA cannot fit on this data set, the system puts the excess on the common page data set. And, if the common page data set gets full, its excess goes to the PLPA page data set. In the interest of good performance, however, you should make the common page data set big enough to prevent its “spilling over” to the PLPA page data set (except in cases forced by error situations). Finally, if both SCM and the PLPA and common data sets are full (or have *NONE* specified) then the system puts the excess on the local page data sets. Spilling PLPA into local page data sets results in the failure of subsequent warm and quick starts. For specific data set size and placement recommendations, see z/OS MVS Initialization and Tuning Guide.

How page data sets are specified: Page data sets are specified by a merging of information from three sources: 1) IEASYSxx; 2) operator-issued PAGE parameter; and 3) the page data sets from a previous cold start. The system merges this information as follows:

From the PAGE parameter in IEASYSxx (an alternate system list):
From the PAGE parameter that is specified by the operator in the current IPL: The system merges this page specification with that in either IEASYS00 or IEASYSxx, but not both. The operator specification of page data sets lasts until the next cold or quick start.
The page data sets previously in use: The system uses information about quick starts and warm starts (IPLs that do not specify the CLPA parameter). If a non-demountable device (such as a 3350) is used for the IPL, the device must be online before the IPL.

Note: Two other conditions are prerequisite for certain warm start or quick start situations:

The local page data sets that contain VIO pages from the previous IPL must be mounted for all warm starts, to make VIO slots available. Otherwise, ASM forces a quick start instead.
The common page data set from the previous IPL must be mounted for both quick starts and warm starts if the system's writing of the PLPA (and extended PLPA) to the PLPA page data set during the previous cold start resulted in spilling some of the PLPA pages into the common page data set.

Usually, page data sets specified by any means must have been allocated, cataloged in the system's master catalog, and preformatted in VSAM format before an IPL can start. You can format the data sets by using the DEFINE PAGESPACE command of access method services (for information about the formatting process, see z/OS DFSMS Access Method Services Commands).

Attention: Do not change or swap the names of systems in the sysplex when using page data set names containing system symbols. If name changes are required, each system in the sysplex must have a cold start IPL.

Syntax examples for the PAGE parameter: Table 1 shows syntax examples of the PAGE parameter and the results they produce.

Table 1. Syntax examples for the PAGE parameter
Syntax	Result
`PAGE=dsname PAGE=(dsname)`	Statements each specify one page data set.
`PAGE=(dsname1,dsname2,dsname3)`	Specifies three page data sets; dsname1 holds the PLPA pages, dsname2 holds the common pages, and dsname3 holds the private area pages.
`PAGE=(dsname1,dsname2,..., dsnamen)`	Specifies `n` page data sets; dsname1 holds the PLPA pages, dsname2 holds the common pages, and dsname3 through dsname`n` all hold private area pages.

The following statement specifies only one page data set:

PAGE=(*NONE*,*NONE*,dsname1)

Storage-class memory (SCM) holds all page types.

Note:

If the operator specifies the PAGE parameter, ASM initialization adds (but does not replace) the data sets as specified. The PAGE data set name list in IEASYS00 or IEASYSxx contains the first named data sets. To ensure that the operator-specified data sets are used for the PLPA and common page data sets, it is necessary to use an IEASYSxx member that contains a null PAGE parameter; one that does not specify page data sets.
It is unnecessary to specify either UNIT or VOLSER because all page data sets must be cataloged in the system's master catalog. ASM initialization therefore does not need externally specified volume serial numbers. The operator can either pre-mount volumes or await a mount message.

Minimum paging space: ASM enforces minimum requirements for paging space. If the requirements are not satisfied, ASM is forced to end the IPL. Additionally, the use of minimum paging space is inadvisable because it can result in poor performance.

Minimum requirements are as follows:

There must be at least a PLPA, a common, and a local page data set to IPL the system. However, *NONE* can be used in place of PLPA and common area page data sets when SCM is used for paging (refer to PAGESCM for details).
The PLPA and common page data sets must be able to hold the total combination of PLPA and common pages (excluding the SQA). If no errors occur, the auxiliary storage space for the PLPA and common page data sets is sufficient if the space equals the size of the PLPA and CSA divided between the two data sets.
If the PLPA and common page data sets spill back and forth because the space is not properly divided between the data sets, performance degradation can result. Severe performance degradation can result if the common page data set is not large enough and, therefore, spills to the PLPA page data set, which is normally read-only after IPL.
Local page data sets are used to hold all private area and VIO pages. The amount of storage necessary varies with each system and can be calculated using the guidelines in z/OS MVS Initialization and Tuning Guide.

Page space shortage: Two warning messages appear when the system resources manager (SRM) detects a shortage of page space, the first when 70% of the available local paging space including SCM, if any has been allocated, and the second when 85% has been allocated. SRM reacts to the situation by preventing the creation of new address spaces. That is, new “start initiator” commands ($SInn), LOGONs, MOUNT commands, and START commands for system tasks that run in their own address spaces do not work. Upon receipt of these messages, you can add paging space to the system dynamically by using the CONFIG SCM,ONLINE or the PAGEADD operator command. For information about using PAGEADD or CONFIG, and for related information about using the PAGTOTL parameter, refer to z/OS MVS System Commands. For these situations, it is valuable to have preformatted, cataloged VSAM paging data sets or offline SCM available. The data sets can be formatted by using the DEFINE PAGESPACE processor of access method services; for more information, refer to z/OS DFSMS Access Method Services Commands.

When the page space usage has been decreased below 70% utilization, SRM informs the operator that there is no longer a shortage.

Value range: The total number of data sets specified must not exceed the combined limit for page data sets on the PAGTOTL= parameter. The data sets can contain system symbols.

Default: None

Associated parmlib member: None

Note: During NIP processing, the system might exhaust SQA and extended SQA if many local paging data sets were specified on the PAGE parameter. If this condition occurs, the value that is specified for the SQA parameter might be set too low. You can increase the SQA value in IEASYSxx.