Steps for setting up the alternate sysplex root for the dynamic replacement of the current sysplex root

About this task

This topic shows how to establish an alternate sysplex root in a shared file system environment.

Before you begin: You need to ensure that the alternate sysplex root does not reside in the same volume, device, and control unit as the current sysplex root.

To minimize the single point of failure, the alternate sysplex root file system should be a different PFS type than that of the current sysplex root file system.

Procedure

Allocate a new file system to be used as the alternate sysplex root file system, following these rules:
1. The UID, GID and the permission bits of the root directory in the alternate sysplex root file system must match the root directory in the current sysplex root file system
2. If the SECLABEL class is active and the MLFSOBJ option is active, then the multilevel security label for the alternate sysplex root must be identical to the assumed multilevel security label of the current sysplex root.
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On the alternate sysplex root, set up the mount points and the symbolic links. The mount points and the symbolic links must be same as the ones on the current sysplex root.
1. Mount the alternate sysplex root file system at a temporary mount point (for example, /altroot).
2. Select one of the following suggested ways to set up mount points and symbolic links:
  - Use the pax shell command to populate the alternate sysplex root file, using the current sysplex root as a source. For example:
```
cd / 
pax -wr -pe -XCM ./ /altroot
```
  - Use copytree to populate the alternate sysplex root, using the current sysplex root as a source. For example:
```
 copytree -as / /altroot
```
  - Manually issue mkdir and ln -s shell commands to create the mount point directories and symbolic links similar to the current sysplex root.
3. Unmount the alternate sysplex root.
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Specify ALTROOT in the BPXPRMxx parmlib member with the mount point in the root directory of the current sysplex root file system.
Restriction: The ALTROOT mount point must not exceed 64 characters in length.
Example: To specify ALTROOT:
```
ALTROOT FILESYSTEM ('OMVS.ALTROOT.ZFS') 
   MOUNTPOINT('/sysalt') PARM ('FSFULL(70,10)')
```
You can use the SETOMVS SYNTAXCHECK operator command to validate the ALTROOT syntax.
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Make sure that all systems in the shared file system environment have direct access to the new file system and can locally mount it.
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Process the ALTROOT statement by using the SET OMVS command or by initializing the OMVS with the updated BPXPRMxx parmlib member. For example:
```
SET OMVS=(xx)
```
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Results

When you are done, you have established an alternate sysplex root in the shared file system configuration. The alternate sysplex root is mounted in read-only mode at the specified mount point and designated as AUTOMOVE. When the alternate sysplex root becomes the current sysplex root, it is mounted in read-only mode and designated as AUTOMOVE regardless of the current sysplex root settings.

Requirement: If you make changes to the current sysplex root after the alternate sysplex root was established, you must make the same changes to the alternate sysplex root as well.