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Datacenter Migration using vSphere Replication


We are planning a datacenter migration using vSphere Replication.  My question is around the cut-over.  We have the VMs replicating just fine.  At cut-over time, our plan is to gracefully shutdown the VMs on the source site, then perform a fail-over using the sync latest changes option.  My assumption is that that will result in zero data loss.  First off, is that assumption correct? 

My second question is if a VM is in the middle of a delta sync and it is gracefully shutdown, will that delta sync complete or will it be cut off?  In other words, do we need to make sure the VM is not in the middle of a snyc before gracefully shutting it down?  One of the VMs is very busy and it is just about continually syncing, one stops and another starts so it would be hard to find a time when it isn't in the middle of a snyc.

My third question is if a VM is NOT in the middle of a sync, but it is still configured for replication so changes are being tracked and it is gracefully shut down, are the changes that have been tracked since the last sync discarded or are they saved so that when we fail-over with the sync latest changes option, it just has to do a normal delta sync?  From what I can find, it seems like those changes that have been recorded, but not sent over are lost when the VM is shutdown and when you do a fail-over using the sync latest changes option, it has to do an offline sync and checksum every block to see if it is different and then send the changes over.  Basically like a fully sync using a seed.  My concern is the time required to do the checksum.  It would be nice if just the changes that were tracked but not yet sent would be sent, but it doesn't sound like it.  Just looking for some confirmation.



1 Reply
VMware Employee
VMware Employee


For the first question, with sync latest changes option, VRMS will invoke creation of an offline instance, before creating the recovery VM image. There is no data loss.

For the second question: If a VM is in the middle of a sync, the sync will be aborted.

For the third question: he replication state is saved in a .psf file for each disk. The offline instance will only sync the changed blocks unless someone changes a disk while the VM was turned off which will end up in VR doing a full sync of that disk.​