Zerto replication is quite easy to configure. Once you have a Zerto Virtual Manager (ZVM) and Virtual Replication Adaptors (VRA) up and running at both sites, you can start adding your virtual machines to replication. There is, however, one question which comes up a lot from the operations point of view. What if you have replication going between the sites and you need to put one of your ESXi hosts into maintenance mode, would that break the replication? The answer is as always – it depends.
Source Site
In Zerto you typically have VRAs installed on each of the hosts at both sites and traffic going one way – from Production data centre to DR. Now, if you want to do maintenance on one of the hosts where VMs are being replicated FROM (Production site) then all you need to do is vMotion VMs to the remaining hosts. Zerto fully supports vMotion and the process is seamless. When VMs are moved to other hosts, VRAs on these hosts automatically pick them up and replication continues without user’s intervention.
Destination Site
If you want to do maintenance on one of the hosts where VMs are being replicated TO (DR site), then this is where you need to be more careful. VMs replicated by Zerto are not shown in vCenter inventory and obviously can’t be moved using conventional vMotion method. This is done from ZVM’s GUI.
In ZVM find the host you want to put into maintenance mode on the Setup tab and in the More drop-down menu select Change VM Recovery VRA. Select the replacement host where you want to redirect VM replication to and click Save. What this option does in Zerto is somewhat similar to what vMotion does in vSphere – it migrates VMs between VRAs.
Once you hit the button, VMs’ RPO will start to grow until the migration is finished. In my case for 12 VMs the process took about 5 minutes to complete. If you have dozens of protected VMs on each of the VRAs, it may take significantly longer. If it’s a concern, you may want to allocate a maintenance windows for this activity.
You will also get a warning that the migration will result in a bitmap-sync. Bitmap Sync tracks the changed blocks on a VM when replication to the destination VRA is interrupted. The amount of changed data over a 5 minute period should be reasonably small. And in my experience VMs get back in sync after a migration very quickly.
When all replicated VMs are moved to another recovery host, you can vMotion out any VMs you may have running on the host, shut down the VRA and put the host into maintenance mode to carry out the maintenance activities.
Once that’s finished, just do the reverse. Disable maintenance mode on the host, boot up the VRA and move back the migrated VMs. In the Change VM Recovery VRA dialogue you can select a completely different set of VMs to move back. As long as you keep them balanced between all VRAs in your cluster you should be good.
Niktips's Blog 