Dell Unity: Upgrading a system that has an advanced replication topology

Summary: This Dell Knowledgebase Article provides details when upgrading a system that has an advanced replication topology.

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Symptoms

Using the example reference figure below (Figure A): 
If you upgrade the primary site A first, the upgrade might make the asynchronous session from the primary site A to backup site C unrecoverable. If you upgrade Site B first, Site B no longer receives the system snapshot from Site A. Also, Site C cannot use a user-created snapshot as a common base during a preserve operation.

Unity_Replication_Requirement
Figure A
 
 

Cause

  • If a Unity array is replicating between pre-5.2 and 5.2 systems.
  • Pre-5.2 systems do not have the Fully Qualified Domain Name (FQDN) feature for locating an LDAP server.
  • Therefore, if a 5.2 system is replicating to a pre-5.2 system, the 5.2 FQDN configuration information is not replicated to the pre-5.2 system. The pre-5.2 system will only have the LDAP server IP addresses.

Resolution

  • Upgrade backup sites BEFORE primary sites
  • Upgrade asynchronous backup sites before synchronous backup sites

If you have an advanced replication topology (fan-out or cascade), you must follow a specific sequence when performing a nondisruptive upgrade (NDU). When you upgrade such a system to UnityOS 5.2, you must upgrade the backup sites before the primary production site. Back up the destination site that has an asynchronous replication session with the primary production site first. For example, primary production Site A has replication sessions with two backup sites, B and C. Site A has synchronous sessions with Site B as the destination. Site A also has an asynchronous session with Site C. To upgrade all these sites to UnityOS 5.2, you must first upgrade Site C, followed by Site B. Finally, you upgrade the primary production Site A.

Unity_Replication_Requirement

Additional Information

Dell Unity: Replication Technologies

 

 

Affected Products

Dell EMC Unity, Dell EMC Unity Family |Dell EMC Unity All Flash, Dell EMC Unity Hybrid
Article Properties
Article Number: 000199194
Article Type: Solution
Last Modified: 13 Aug 2025
Version:  7
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