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VMWare Migration VS Cloning a VM?  Which is faster?

Posted on 2015-02-06
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Last Modified: 2015-02-09
I was manually migrating a VM in vcenter from one modern host to another and it was blazing fast, at around 800Mb/s.  I tried to clone another VM in the opposite direction, but between the two same hosts and it was much slower at around 200Mb/s.

So I am wondering, is cloning for some reason slower the migrating?  And if so, note that the only reason I chose to clone was I was worried that I may need to cancel the process before it had completed.  So my second question is, can a manual migration be canceled part of the way through the process without messing up the VM at its original location?  IE, at what point during the migration does it delete the machine from its original destination?  I am worried that a cancel migration will leave two botched VM fragments on 2 hosts, with both of them being somehow incomplete and unusable.

Note, I needed the option to cancel the process and the the second VM needed to be backup in within 1.5 hours, and if not, I had to be able to back out of it.

Thanks.
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Question by:CnicNV
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by:Vaseem Mohammed
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If I understood your scenario and question, 1st case was vMotion, as both host is sharing the same datasore the migration moved the configuration file to a different host and not the virtual hard drives.
2nd case, cloning, its same host or different host a COPY of virtual hard drive is made and hence it takes time. The speed of clone depends on storage, LUN, network.
Cloning will not make changed to original VM and cloning process does NOT delete the original VM.
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by:CnicNV
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The two hosts do not share the same data store via a SAN or anything like that, rather the the VM exist locally on the hosts locally hard drives.
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Carlos Ijalba earned 500 total points
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You can cancel ANY process in VMware and won´t leave botched fragments behind, the only times that I have seen fragments behind have been caused by backup programs when doing snapshots to be able to back up VMs, then failing the backup and not cleaning behind themselves.

Basically, when you cancel a process, VMware will wait until it can safely cancel it, which usually implies waiting for the actual transaction to finish to be able to rollback whatever has done, therefore canceling a migration  will take nearly as long as actually doing the migration (once the data has started to move), so might as well wait until it finishes correctly.

VMware at the end of the day will send orders to whatever it has underneath like a SAN or a NAS, to do a block write, once that operation has finished the SAN or the NAS will give the control back to VMware, until then it doesn´t have much control to cancel the operation.

Looking at your timings between machines, what it looks like is that machine 2 is simply faster than machine 1 on disk writes.
To be able to measure the migration and the clone activity faithfully, you should do at least 3 runs of migrations and 3 runs of clones and compare all results, and they should all be on the same direction, as otherwise you won´t be comparing the same operation or hardware unless both ESXi servers and network setups are identical.
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by:gheist
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The only fast stuff is cloning a VM on datastore that supports VAAI.
Rest reads all data to ESXi and writes to new place.
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by:CnicNV
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Perfect and detailed answer, yes, now that you mention it, "machine 2" has a higher grade PERC controller where as the other does not, so that's probably the difference.

Thanks again.
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by:gheist
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There is no VAAI support in your setup. So no fast fast clone.
As load reduces on old array the last machines will go out faster. So start with small disks, then go to big ones...
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