IT Systems Engineering

How to re-sync replication with an old initial replica on USB drive

I ran into a situation where a large VM had its replication enabled, and the initial replication (IR) sent to a USB drive. Then IR was imported on the DR site. Everything was fine but later on, for one reason or another, the replica was deleted. At this point you have the option of recreating another IR to a USB drive, sending that USB drive to your DR site, importing the new IR again. All that, of course, will take quite a lot of time.

The alternative is to import the same old IR on the USB drive (assuming it is still there at the DR site) and letting the replication sync up the changed bits.

Here is how to do that.

1. enable replica of ABC from primary site.
let the initial replica go to USB or to the network, does not matter, We will stop it in a minute.

2. From the primary site, stop replication using “Cancel initial replication”

3. This will leave the replica VM on the DR site intact.

4. Now, on the DR site, choose the option “Import initial replica”, wait for that to finish.

5. On the DR site, remove replication. Now it becomes a regular VM on the DR site. This step is needed to make the DR site ready to accept new replication from Primary site.

6. Then on the Primary site, choose the “Start Initial Replication” and click on the “existing VM on the replica server” option. It will detect the existing VM on the DR site and start IR.

7. Actually, it will start a block level resynchronization operation, as evidenced by entries in in the Hyper-V’s VMMS log, which read like this:

Starting resynchronization operation on VHD ‘C:\ClusterStorage\Volume1\vm_name\vm_name_DISK_1.VHDX’ of VM ‘vm_name’. Starting Block = ‘0’. Total blocks = ‘29622272’. (Virtual machine ID FA8190AC-B2D5-460C-BBAA-5F85EB999DF7)

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