Must you Configure VSS Shadowstorage in a Guest OS to Use VMWare App-consistent Snapshots?

Bill Bach
Bill Bach used Ask the Experts™
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I am trying to track down what should be an obvious question, but one which seems to be ignored on the 'Net:

When you enable an application-consistent backup in VMware, it configures the VMware Tools component inside the guest operating system to take a VSS Snapshot, which then engages all of the active VSS Writers to ensure that all data write activity has been quiesced prior to the backup.  This is all the easy part.

Now for the hard part: What happens if the system administrator never sets up shadowcopy storage within the OS?  Or, more directly, do you need to configure the operating system's VSS storage (i.e. vssadmin list shadowstorage) in order for this to work?  I have seen references that VMware handles the snapshot duties, which would seem to imply that you do NOT need shadow storage configured.  However, I can also see where the VSS environment within the guest OS would depend on it, and it might refuse to allow a VSS snapshot to occur without storage being available.  Which is it???
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VMware and Virtualization Consultant
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Commented:
You do not need to do anything in the VM. VSS should already be configured and working as part of the OS.

Make sure VMware Tools is installed in the VM, which it should always, and that's it.

Backups will then just happen, and quiesce the VM, if required.
Bill BachPresident and Btrieve Guru

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Commented:
So does that imply that the OS never actually has the shadowcopy in place at all for any length of time?  It sounds like this could ONLY work if the VMware backup requests the snapshot, the VSS writers all quiesce the disk, tell the OS to go ahead with the snapshot, and then the VMware backup immediately releases the guest OS snapshot, relying instead on the VMware change block tracking mechanism.  Does that sound right?
Andrew Hancock (VMware vExpert / EE Fellow)VMware and Virtualization Consultant
Fellow 2018
Expert of the Year 2017

Commented:
Yep

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