How to Perform Host Maintenance Without Affecting Replication

KB Number:
000001703

Symptoms:


With VRA Maintenance Mode deprecated (see Why Can I No Longer Access VRA Maintenance Mode?), an administrator may want to know how to perform host maintenance without affecting replication.  This article explains how to use the Change Host feature, introduced in 2.0 Update 4 (Zebra), to provide similar functionality.

 

Cause:
VRA is a source VRA
 
  • If an administrator vMotions source VMs to other VRAs/hosts in the source cluster, host/VRA maintenance can be performed without any interruption in replication - no syncs whatsoever.
  • If an administrator does not vMotion source VMs, following host/VRA maintenance, associated VPGs will enter Delta Sync.
VRA is a target VRA
  • If an administrator uses the Change Host functionality (see How to Perform Host Maintenance Without Affecting Replication) to change the target host for each VM within each VPG currently using the host to undergo maintenance as a target, host/VRA maintenance can be performed without any interruption in replication - no syncs whatsoever.
  • If an administrator does not use the Change Host functionality to change the target host for each VM within each VPG currently using the host to undergo maintenance as a target, following host/VRA maintenance, associated VPGs will enter Bitmap Sync.  Note that if this occurs, affected VPGs will still be in a Protecting state, and will be recoverable, if the duration of the host/VRA maintenance is not greater than that of the CDP History configured and available.
VRA is a source target VRA
 
  • If an administrator vMotions source VMs to other VRAs/hosts in the source cluster, and uses the Change Host functionality (see How to Perform Host Maintenance Without Affecting Replication) to change the target host for each VM within each VPG currently using the host to undergo maintenance as a target, host/VRA maintenance can be performed without any interruption in replication - no syncs whatsoever.
  • If a customer does not vMotion source VMs to other VRAs/hosts in the source cluster, following host/VRA maintenance, associated VPGs will enter Delta Sync.
  • If a customer does not use the Change Host functionality, to change the target host for each VM within each VPG currently using the host to undergo maintenance as a target, following host/VRA maintenance, associated VPGs will enter Bitmap Sync.  Note that if this occurs, affected VPGs will still be in a Protecting state, and will be recoverable, if the duration of the host/VRA maintenance is not greater than that of the CDP History configured and available

Solution:
The Change Host feature, introduced in 2.0 Update 4 (Zebra), allows an administrator to nondestructively reconfigure VMs within a VPG to use different target hosts.  Prior to 2.0 Update 4 (Zebra), attempting to do so would result in new target volumes being created under the new target host, resulting in an Initial Sync.  Instead, with 2.0 Update 4 (Zebra), once saved, the VPG will update, the relevant VRAs will reconfigure, and the VPG will re-enter the Protecting state.
 
Instructions for using the Change Host feature via the Zerto Virtual Replication GUI are as follows:
  1. Use the Resource Report to determine which VMs are currently using a given host as a target.  For instructions on doing so, see Which VMs Are Configured to Use A Particular Host As a Target?.
  2. Edit the relevant VPG by selecting Actions > Edit in the VPG details screen, or choosing the pencil icon inline with the VPG in the VPG List screen (or in the VPGs tab in ZVR 3.0 and later.)
  3. Select a VM within the VPG, and choose Configure.
  4. Change the Recovery Host field to the desired value, and click Save.
  5. Change any other necessary VMs' recovery hosts, and click Save to save the changes to the VPG.
Note: Changing the "Recovery Host" value under the "Default Values" area of the Manage VPG screen will only change this value for newly added VMs.  All previously configured VMs within the VPG need to be selected one-by-one, and need to have the above procedure performed.

Starting with 3.0 Update 1, PowerShell Cmdlets are added allowing the scripted identification and change of VMs' target hosts.  For more information on these, refer to the following online documentation:
 


Affected Versions:
2.0 Update 4 (Zebra) and greater.

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