Will vm snapshot include data on additional disks

[karthijk]

My environment is vcenter and i have created 3 additional disks for my vm. 

Now if i take vm snapshot. will it include data of those 3 additional disks as well in the snapshot ?

What data will be available in the snapshot?

[NathanosBlightc]

Yes, of course. Whenever you generate a snapshot of a VM, this operation will affect all of the virtual disks (VMDK files). Regardless of snapshot files(*.vmsn and *.vmsd), snapshot generation causes to produce delta disks that are like the child disks for their parents (initial VMDK files). For more information I will suggest reading my blog post:

https://virtualundercity.blogspot.com/2019/08/virtual-machine-snapshot-details.html

[scott28tt]

So long as the disks are not set as “independent” they will be included in your snapshot.

A snapshot is a point in time state of the VM that you have the option of reverting to if you want to.

The typical administrator use is to take a snapshot, make some change to the VM OS/applications/data that you think you might want to undo, delete the snapshot of you don’t need to revert the VM state back to the point where you took the snapshot.

They are also used temporarily by VM backup tools to have a consistent state while allowing the VM to continue to run, snapshots taken by backup tools are deleted by those tools at the end of a backup process.

What is your use case for wanting to use snapshots?

[karthijk]

We also use snapshots to revert back to known state during patching and other activities.

We missed to delete a snapshot and now it has grown very large in size because of which we are facing IO related issues.

Wanted to know what data are in the snapshot as the size became huge(Near to TB). 

We have some nfs mount points and other disks attached to linux vm. although root vg is very small we doubt if these nfs and other non-root disks also included in snapshot.

how do we identify the disks are not set independent?

[scott28tt]

Taking a snapshot really does 2 things:

1. A copy of the VMs memory is written to a file.
2. Each virtual disk file is set as read-only and all subsequent writes go to a delta file created for each virtual disk.

If you delete the snapshot the memory file will just be deleted and the contents of the delta files will be written back to the original disk files - you are deleting your ability to be able to revert to that snapshot.

Disks are not independent by default, you can check them by looking at the properties of each one in the VMs settings.