How to use synchronization

[dhatfield]

Hi Guys,

I am doing a migration of Vms from VCenter/ESXi to Hyper-V. I have just finished testing how to use the synchronization feature. I can't find any documentation on it.
From what I can see. It performs a snapshot on first copy, it then copies the initial disk (on my system it is copying at approx 410Mbps). Once the initial copy is completed, it creates a 2nd snapshot, it then runs a new copy which runs about 25% quicker. Once the 2nd copy is finished, the process is complete but there is only one VHDX file on the Hyper-V end so it looks like it has merged the data from the 2nd copy on the fly. Is this correct?
Also, my original disk was 60GB and the snapshot was only 1GB but the time to copy was 20mins for the 1st copy and 15mins for the 2nd copy.
Am I reading this right? I am trying to understand the use case for this.
NOTE: I have a couple of servers that are approx 2-3TB so synchronization may be a good fit but if the 2nd synch only performs 25% quicker and finishes after one snapshot and doesn't shutdown the original VM and startup the new VM then this function may not do what I need.

[yaroslav (staff)]

You can convert the VM live and it will make snapshots to let the destination catch up with the changes you made.

[dhatfield]

Hi Yaroslav,

But from what I could see, it only does this once and it doesn't shut down the original VM so if the job completes and you haven't manually shut down the original VM then you need to rerun the job from scratch.

I thought that you could run it and it would continue making snapshots until such time as you power off the original VM and then it will complete the final pass.....

Is this not how it works?

[yaroslav (staff)]

Hi,

You do not need to power off the VM. There is only one snapshot taken and then is merged to the source so everything written to the VM during conversion is not lost.

[nroot]

Hello, I am preparing for my first migration from VMware to HyperV using the great V2V converter tool and I am gathering theoretical knowledge.
However, I do not understand the answer regarding additional synchronization during live transfer. If the live transfer is successful, which will take about 2 hours, then synchronization will take place, which will merge the changes on the source machine that occurred during the live transfer and which may take several minutes. However, if during this time the source machine remains active as production and is not shut down, changes will still occur on it that the synchronization run will not reflect.
So if the source machine is not shut down before synchronization, how is it possible for the target machine to be completely identical 1:1 to the source machine, whose state will change every second?
Or is the synchronization principle different?
Thank you in advance for any answer.

[yaroslav (staff)]

Welcome to StarWind Forum.
Synchronization stage is where the destination VM catches up with the source. When conversion starts the snapshot is created and tracks the data changes during conversion. This snapshot merges during replication phase so the source and destination both end up with the same data.

[k2cooper]

Hi,

I was going to post a similar question and am glad I'm not the only one baffled by this. Any changes that occur during the second "catchup" synchronization, unless I'm missing something, won't be on the final vm on the new server. There's now a server that's running (the source) and a copy of the server (the target) that's off. It seems to me that the only way to ensure the new vm exactly matches the old is o to shut down the old at some point before the second synchronization begins. Is this not the case?

And if it IS the case, is there a way for v2v to automatically shut down the source before doing the second synchronization so I don't have to try and time it so I;'m sure I'm awake and available when the first synchronization is 95% - 99% complete?

Thanks.

[yaroslav (staff)]

Any changes that occur during the second "catchup" synchronization, unless I'm missing something, won't be on the final vm on the new server.

That's wrong. The snapshot phase exists so that the changes will be present in the target.

[TwiceOver]

Any changes that occur during the second "catchup" synchronization, unless I'm missing something, won't be on the final vm on the new server.

That's wrong. The snapshot phase exists so that the changes will be present in the target.

I'm really confused by this feature. I remove VMWare Tools then ran a V2V migration to Hyper-V using the "synchronize" option. It did the initial snapshot and copy. It then did another snapshot and copy. Then it left the ESXi VM running and a completed powered off VM in Hyper-V. Shouldn't it have turned off the ESXi VM or at least disconnected the network prior to the final sync?

[yaroslav (staff)]

You are right, ideally, the software should have taken down the source VM and started destination one. However, V2V Converter still can't do that yet, it is on the project's roadmap though.

[TwiceOver]

You are right, ideally, the software should have taken down the source VM and started destination one. However, V2V Converter still can't do that yet, it is on the project's roadmap though.

Thanks. It isn't a big deal, I can handle the down time. Just thought it would be really neat if it worked as a fully "hot" migration.

[yaroslav (staff)]

100%
I hope to finally see it in converter one day.

[k2cooper]

So the only way to have minimal down time while getting an exact copy in the HyperV is to shut down the esxi VM prior to (or during) the final sync? There's no way to have v2v prompt with something like "Ready for the final sync, shut down the source VM then hit continue?" I guess that's what I'm looking for: a way to keep the original up and running as long as possible then shutting down when I'm ready, not having to get when the progress bar will finish.

[yaroslav (staff)]

We plan to shut down the source and start the destination VM in the future. For now, though, shutting down the VM during the snapshot sync is the safest way to ensure that source and destination have the same data.

[SGUZMAN7]

I spent 5 hours Synchronizing and then it complete. How do i get it to take snap and synchronize again? Do i just run the job again until i can shutdown the server?