Sunday, 8 November 2015

Excluding certain VMDKs from Snapshot in VMware

Written by Suhas Savkoor



How to Perform Selective Snapshot of a VM.

Sometimes, we will have a VM with multiple VMDKs, and there comes a need when we have to take a snapshot of this VM. However, we only want to snapshot certain VMDKs.

How do we do this?

1. Power off the virtual machine
2. Delete any existing snapshots before you change the disk mode (Snapshot Manager > Delete All)
3. Right-click the virtual machine and select Edit Settings
4. Select the hard disk that you want to exclude and change the mode to Independent Persistent

Here Independent mode is of two types:

Persistent:
When a VMDK is configured in Independent Persistent Mode, what you will see is that no delta file is associated with this disk during a snapshot operation. In other words, during a snapshot operation, this VMDK continues to behave as if there is no snapshot being taken of the virtual machine and all writes go directly to disk. So there is no delta file created when a snapshot of the VM is taken, but all changes to the disk are preserved when the snapshot is deleted.

Non Persistent:
When a VMDK is configured as Independent Non-persistent Mode, a redo log is created to capture all subsequent writes to that disk. However, if the snapshot is deleted, or the virtual machine is powered off, the changes captured in that redo log are discarded for that Independent Non-persistent VMDK.

Here we want the data to be retained after a Power OFF for the snapshot VMDKs. Hence, we choose Persistent mode.


Enjoy Snapshot'ing