Downgrading PowerPath from 6.x to 5.x

When you downgrade PowerPath from 6.x to 5.x, you need to put aside the PowerPath 5.x saved configuration files in advance.

• Copy contents of /etc/emc/archive of the old PowerPath to another folder such as /tmp/pp_config_backup.
  Note that the files under /etc/emc/archive were created when you upgraded to the new PowerPath.

  # mkdir /tmp/pp_config_backup # cp -p /etc/emc/archive/* /tmp/pp_config_backup

• Uninstall the new version of PowerPath.

  # rpm -e EMCpower.LINUX-6.1.0.00.00-091.el5

• Delete contents of /etc/emc/archive folder since that now contains config files updated by the new PowerPath version.

  # rm -f /etc/emc/archive/*

• Install the old PowerPath version.

  # rpm -ivh EMCPower.LINUX-5.6.0.00.00-143.RHEL5.x86_64.rpm

• Copy the backed up contents from first step to /etc/emc/archive folder.

  # cp -p /tmp/pp_config_backup/* /etc/emc/archive/ # cp -p powermt.custom /etc/emc/archive/powermt.custom.saved # cp -p emcp_registration /etc/emc/archive/emcp_registration.saved

• Start PowerPath. While starting, PowerPath will automatically restore the config files from /etc/emc/archive and the old settings will be restored.

  # /etc/init.d/PowerPath

Installation and Administration Guide touches on how to bring the saved configuration settings back as follows.

If issues are observed during or after starting PowerPath and if the old
PowerPath version needs to be restored, the following steps should be done to
preserve the saved configuration settings:

a. Copy contents of /etc/emc/archive to another folder such as
/tmp/pp_config_backup.
b. Uninstall the new version of PowerPath.
c. Delete contents of /etc/emc/archive folder since that now contains config files
updated by the new PowerPath version.
d. Copy the backed up contents from step a to /etc/emc/archive folder.
e. Start PowerPath. While starting, PowerPath will automatically restore the config
files from /etc/emc/archive and the old settings will be restored.

However if you need to downgrade between two major releases (say, 6.1 to 5.6), some file format can be different.
This is why you need to do additional file backup/restore. 
        5.x     /etc/powermt.custom
        6.x     /etc/powermt_custom.xml