VMware vCenter in Enhanced Linked Mode pre-changes snapshot (online or offline) best practice
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VMware vCenter in Enhanced Linked Mode pre-changes snapshot (online or offline) best practice

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Article ID: 313886

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Updated On:

Products

VMware vCenter Server

Issue/Introduction

When using multiple vCenter Server Appliances (VCSA) in the same Single Sign-on Domain, replicating in Enhanced Linked Mode (ELM), there is high potential of corruption of the domain if snapshots of the appliances are taken while they are in running state. Use of offline snapshots in ELM deployments is very strongly recommended for a safe rollback point. This means all appliances should be gracefully shut down, and snapshots need to be taken while the VCSAs are in powered off state (at the same time).

If any change must be reverted, restore all of the nodes in the ELM deployment to this offline/consistent snapshot state. Only start powering the restored nodes back on after all of them have been restored from the snapshots.

Doing otherwise can and will introduce inconsistencies between the local VM Directory instances of the embedded platform service controllers, which will prevent the nodes from successfully replicating with each other.

Notes:

Environment

  • VMware vCenter Server Appliance 6.x
  • VMware vCenter Server Appliance 7.0.x
  • VMware vCenter Server Appliance 8.0.x

Cause

vCenter Servers using ELM replicate their vmdir database changes to one another every 30 seconds.

If snapshots of vCenter Servers are created without them being powered down they will be an in uncertain replication state even when queisced.

Also, when reverting just one vCenter Server from snapshot and not others they may restore with different synchronization states, which can cause much additional work to manually synchronize the vmdir database. And sometimes this can even cause problems with the vmdir database that cannot be repaired

Resolution

As stated above, VMware recommends to have offline Snapshots (virtual machine powered off) of all nodes in the same SSO domain, aka running in ELM replication, before any activity that will include changes in the vCenter Server.

Offline snapshots of all nodes in an SSO domain (ELM) are required when any SSO domain update will be performed. This includes but is not limited to:

  • vCenter Server Updates (Full Version, Update Release, or Patch Release).
  • Using the lsdoctor tool to make any changes.
  • Adding a new vCenter Server to an existing SSO domain.
  • Retiring a vCenter Server from an existing SSO domain.
  • Certificate Replacement (Machine, CA, STS, etc).


Any read only activity does not require offline snapshot. That means the below activities can be performed with NO need for snapshot (Neither online nor offline). 

  • vCenter Server / PSC backups.
  • Using the lsdoctor tool  with the --lscheck parameter.
  • Using the checksts script.

Caution:

  • Offline snapshot is a MUST when using lsdoctor tool unless using the --lscheck switch (only) which is used to check for common issues in the lookup service.
  • Make sure there is no backup task running before taking the snapshot of the vCenter Server or the PSC.
  • Do not take snapshot of the vCenter VM(s) if it’s part of vCenter High Availability (VCHA) configuration. 



Additional Information