Processor storage amount

z/OS® supports an architectural limit of 4 terabytes (TB) of processor storage per logical partition (LPAR). However, the actual amount of processor storage that is supported per server and LPAR varies, depending on the IBM® server.

Table 1 shows the maximum amount of processor storage that is supported by z/OS for each of the IBM servers.
Start of change
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
Start of changez15™End of change Start of change40.0 TBEnd of change Start of change4 TB, as of z/OS V2R2End of change
Start of changez14™End of change Start of change32.0 TBEnd of change Start of change4 TB, as of z/OS V2R2End of change
z14 ZR1 8.0 TB 4 TB, as of z/OS V2R2
z13® 10.0 TB 4 TB, as of z/OS V2R2
z13sTM 4.0 TB 4 TB, as of z/OS V2R2
zEC12 3.0 TB 1 TB, as of z/OS V2R1
zBC12 496 GB 128 GB, as of z/OS V2R1
End of change
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

Start of changeFor z/OS V2R4 with the z15™ or z14™ server, a minimum of 8 GB of processor storage is required. When running as a z/VM guest or on an IBM z Personal Development Tool (zPDT), z/OS V2R4 requires a minimum of 2 GB of processor storage.End of change

To assist your installation with upgrading from Start of changez/OS V2R2 or V2R3End of change, IBM provides a new health check that issues a warning for a system that is configured with less than 8 GB of processor storage.

Start of changeIf you attempt to IPL z/OS V2R4 on a z15™ or z14™ server (including the ZR1) 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. If you attempt to IPL z/OS V2R4 on an earlier IBM server, no warning message is issued.End of change

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.