Processor storage amount

z/OS 3.1 supports a limit of 16 terabytes (TB) of processor storage per logical partition (LPAR). The actual amount of processor storage that is supported per server and LPAR varies, depending on the IBM server. If more than 4 terabytes (4 TB) is defined to a z/OS LPAR, by default all memory beyond 4 TB is part of the 2 GB large frame area. For information about the large frame area and the associated LFAREA parameter, see z/OS MVS Initialization and Tuning Reference. Storage reconfiguration is disabled for systems with more than 4 TB of processor storage that is defined as part of the 2G Large Frame Area.

Start of change Alternatively, your installation can define the memory above 4 terabytes (4 TB) as Dedicated Memory. Dedicated Memory is assigned directly to applications and can be used as 2G, 1M, and 4K frame units to back only high virtual private storage. Additionally, Dedicated Memory can be configured offline and does not preclude nonpermanently resident storage below 4 terabytes from being reconfigured offline. For more information about Dedicated Memory, see z/OS MVS Initialization and Tuning Guide. End of change

Table 1 shows the maximum amount of processor storage that is supported by z/OS for each of the IBM servers.

Table 1. Maximum amount of processor storage supported by z/OS
IBM server	Maximum amount of processor storage per IBM Z server	Maximum amount of processor storage per z/OS LPAR
IBM z17® machine type 9175	40.0 TB	16 TB, for z/OS V2R5 and later
IBM z16® machine type 3931 (model A01)	40.0 TB	16 TB, for z/OS V2R5 and later
IBM z16 machine type 3932 (all models)	16.0 TB	16 TB for z/OS V2R5 and later
IBM z15® machine type 8561 (model T01)	40.0 TB	16 TB for z/OS V2R5 and later
IBM z15 machine type 8562 (model T02)	16.0 TB	16 TB for z/OS V2R5 and later
IBM z14 (all models)	32.0 TB	16 TB for z/OS V2R5 and later
IBM z14 ZR1	8.0 TB	8 TB for z/OS V2R5 and later

For the storage amounts:

1 TB equals 1,099,511,627,776 bytes.
1 GB equals 1,073,741,824 bytes.

Minimum processor storage amount for IPLing a z/OS system

To run z/OS 3.1 on a supported IBM server, a minimum of 8 GB of processor storage is required to IPL. When running as a z/VM guest or on an IBM z Personal Development Tool (zPDT), z/OS 3.1 requires a minimum of 2 GB of processor storage.

If you attempt to IPL z/OS 3.1 on an IBM server with less than the minimum amount of processor storage, z/OS issues a warning WTOR message during IPL. Continuing with less than the minimum amount of processor storage might impact the availability of your system.

For earlier combinations of z/OS systems and IBM server models, smaller amounts of processor storage might be required for IPL. The minimum amount of processor storage that is required to IPL a z/OS system depends on various factors, including the following:

Number of devices in the I/O configuration
Number of address spaces to be created
Types of applications to be supported
Products and subsystems to be supported.

In internal tests that were conducted at IBM, it was found that 256 MB of processor storage was the minimum amount required to IPL a z/OS V2R2 system. The test systems were IPLed to the point of initializing the JES2 subsystem, and had I/O configurations that were defined with the following devices:

51168 direct access storage devices (DASD)
16 graphics devices
5127 channel-to-channel (CTC) connections
52 tape drives.

An actual production system is likely to require more than 256 MB of processor storage for normal operations.

For any release of z/OS, it is recommended that you monitor your processor storage usage, and determine whether to add more for better execution of workloads. The minimum stated here is not a likely environment for many installations, however, it has been observed that many systems perform adequately with 8 - 16 GB of processor storage, depending on the workload and system definition. A good indication that you have chosen an acceptable processor storage amount for your system is if no paging occurs, or if the amount of paging that occurs is within your service level objectives.