Add or change volumes to keep your z/OS root file system in a single data set

Description

Because of release enhancements and service, the size of the z/OS root file system (or version root file system) continues to grow from release to release. The size of the z/OS root file system, whether HFS or zFS, is expected to closely approach, if not exceed, the limit of 3339 cylinders on a 3390-3 device.

It is advisable to have the z/OS root file system within a single data set for ease of management.

Note: As of z/OS V2R1, there is another file system delivered with z/OS, the font file system. See z/OS Planning for Installation for information about the size and contents of this file system.

Table 1 provides more details about this migration action. Use this information to plan your changes to the system.

Table 1. Information about this migration action
Element or feature:	Multiple.
When change was introduced:	General migration action not tied to a specific release.
Applies to migration from:	z/OS V2R1 and z/OS V1R13.
Timing:	Before installing z/OS V2R2.
Is the migration action required?	No, but recommended for ease of management if your z/OS root file system resides on a 3390-3 volume (or another DASD volume that is close to the 3390-3 limit of 3339 cylinders).
Target system hardware requirements:	None.
Target system software requirements:	None.
Other system (coexistence or fallback) requirements:	None.
Restrictions:	None.
System impacts:	None.
Related IBM® Health Checker for z/OS® check:	Use IBM Health Checker for z/OS check CHECK(IBMUSS, ZOSMIGREC_ROOT_FS_SIZE) to determine if a volume has enough space for the z/OS root file system.

Steps to take

To keep the z/OS root file system in a single data set, do one of the following:

Move your z/OS root file system to a larger DASD volume geometry
Use multiple volumes for the z/OS root file system data set.

If your z/OS root data set cannot fit on the volume or volumes you have defined for it, divide the z/OS root, with the smaller file systems being managed together.

Remember that all systems to which you deploy the z/OS root file system need sufficient DASD space to hold the z/OS root.

Tip: File systems for subsystems and products other than the z/OS product itself might also increase in size. When examining the volume for how much space your z/OS file system is using, check other product file system sizes too.

Reference information

For more information about multivolume data sets, see z/OS DFSMS Implementing System-Managed Storage.