Migration...Explained.

[AmazingTed]

Hi, back again for some advice...

Looking if someone can try and explain the three methods of migration offered for VM's inside vCenter.

Below i have tried to summarize my understanding, looking for confirmation as to whether its correct or not

Change VM's Host - vMotion

To move the VM's resources ie. CPU and memory to another host but leaving the VMDK file in the original datastore (Which the new host has to have access to). This i am not sure on as i don't understand how you can move a VM without moving its VMDK file?

Change VM's Data Store - Storage vMotion

Change the Data Store where the VM's VMDK file is stored. Leaving the VM on the original host for resources such as CPU and memory, again still a bit confused as with the previous method RE not moving VMDK files.

Change VM's Host and DataStore - vMotion & Storage vMotion

Change the host and the datastore on which the VM resides.

Can anyone clear this up for me? Can you move a virtual machine to another host without moving its VMDK file? If so is my summary correct in that you are relocating it to another host solely to make use of the new hosts CPU and memory etc?

Looking online on i think the answer is that when you copy a VM to another host, you are copying the config files and memory which tell the host how much resources should be allocated to the VM in terms of CPU and memory and nothing to do with the VMDK hard disk file...

Thanks in advance!

[a_p_ · Accepted solution]

You are understanding this correctly.

For vMotion it's necessary that both hosts - source and target - have access to the same shared datastore (e.g. on a separate FC/iSCSI/NAS storage system), so there's no need to copy any files.

Storage vMotion only moves the virtual machine's files to another datastore, which is accessible from the same host. It's like moving a piece of paper from the left to the right. For the guest OS itself this is completely transparent. Changing the host and the datastore together is more challenging, but works on the Hypervisor/ESXi layer and is still completely transparent to the guest OS.

Prior to starting a migration, a validation process will check whether sufficient resources are available on the target host and/or target datastore.

André

[AmazingTed]

So i can move a VM to another host without moving its VMDK HDD file, even if it only has the one?

[a_p_]

Yes, that's what vMotion was made for. As long as the target host has access to the same datastore/.vmdk file this will work just fine.

André

[AmazingTed]

And presumably this is how DRS works, using vMotion?

[a_p_]

Exactly!

André