VMWare workstation 15 - Powered on snapshots?

[whorsfall]

Hi,

In general I have powered down my VM's first then taken snapshots. Obviously you can take snapshots when machines are powered on. When doing this I notice it takes time to finish saving state. So hypothetical situation.

1. VM Powered on (with VMWare tools installed).
2. Take snapshot at 2pm
3. VMWare starts saving state.
4. I keep using VM and save a file to disk and make other changes @ 2:03pm
5. State finishes saving at 2:05pm.

Questions:

1. Is the disk an memory that is saved what it is a 2pm - so my disk will not have changes made at 2:03pm. In other words it is exactly at the instance when I click on save snapshot. (From my testing it is looking like it is from the instant of snapshot). I wanted to be sure this is expected behaviour.

2. In general am I safe to keep using the VM while it is taking the snapshot?

3. How does VMWare keep up and not cause an incosistancy. Does it use VSS for example on a Windows host.

4. Is what saved to disk a differential between the current state and its parent state?

My questions are seeking a futher understanding of how it works so the more info the better

Thanks,

Ward.

[wila · Accepted solution]

Hi Ward,

1. The disk (and memory + CPU registers state etcetera.. ) that are stored in the snapshot are from 2pm

2. Yes it is safe to keep using the VM during the snapshot.

3. It does not use VSS, instead it creates a new set of virtual disk files that store the differences starting at 2pm. Besides that it also stores the contents of the VM memory and VM state

4. That's correct.

VMware snapshots are pretty reliable because it not only stores the disk, but also state. This works well as long as you restore the snapshot on the same host.

My VM backup software Vimalin (see my signature) depends on exactly this to make it possible to create automated backups while your VM is running.

Hope this helps,

--

Wil

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[continuum]

If you want to see how this works in detail then remove the latest vmware.log and reproduce the scenario:

create a new snapshot and write down the time.

In the new vmware.log you get you can see how Workstation interacts with the vmware-tools.

You will also see that Workstation "stuns" the guest before it switches from basedisk to the new snapshot.

When the switch is done you will also see that the guest gets "unstunned"

So in the moment of the switch the VM is "sedated" and will not do anything at all.

I can show you this in more details if you provide the new vmware.log and your notes of the time of the actions.

Ulli

[whorsfall]

Hi,

Great answers - thankyou both,

Ward