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I'm sure many of you have seen the new Snapshot > Consolidate option in the drop-down menu of Virtual Machines in vSphere 5.0, and are probably wandering what the use case is. If you haven't seen it, here it is:

Consol1

The reason this feature is introduced is to address a rather large supportability issue. Occasionally we saw where a snapshot commit/delete operation request would not merge the snapshot delta files with the VMs base disk (what we term a consolidate operation). Unfortunately, this failure to consolidate was not apparent via the UI, and usually only became noticeable to the end user when the delta files grew very large, possibly resulting in a full VMFS or NFS volume if they were attached to very large VMs. Support engineers from GSS (VMware's Global Support Services) would then have you use their many tricks of the trade to consolidate the snapshot deltas into the VM base disk. The issue is that although support resolves most if not  all of these cases, it is a very time consuming & repetitive task.

This new option allows end-users, in the event of a consolidate failure, to do the consolidate operation for themselves without opening a Service Request with VMware. But how do we know whether a consolidate was successful or not? Well, if a commit/delete operation doesn't manage to merge the snapshot delta disks into the VM's base disk, a new warning is surfaced in the UI as shown here:

Needs-consol

An administrator can now use the Snapshot Consolidate option to merge them.

Can I test it?

There is a way to test this via the PowerCLI if you so wish. We now ship the RemoveAllSnapshots method with an option to not consolidate snapshots when it is invoked. The steps to test are quite simple:

  1. Select a VM & manually create a snapshot on it.
  2. Launch vSphere 5.0 PowerCLI
  3. At the PowerCLI prompt, type $VM = get-VM <VM_Name> | Get-View where <VM-Name> is the name of the VM with the snapshot.
  4. At the PowerCLI prompt, type $VM.RemoveAllSnapshots(0) where the boolean value 0 represents the directive to not consolidate.

A 'Configuration Issue' warning should now be surfaced in vCenter, same as that shown above. If you login to the ESXi shell, and examine the home folder of the VM, you will notice that the snapshot delta file still exists. Also, if you examine the contents of the .vmsd (snapshot descriptor) file, you will notice that it contains a new parameter snapshot.needConsolidate = "TRUE".

You can now use the UI to select the VM > Snapshot > Consolidate. This will pop-up an "are you sure" type message. Click yes, and the snapshot delta(s) will be merged with the VM base disk.

R-u-sure

And of course you could also consolidate the delta disk(s) using PowerCLI using $VM.ConsolidateVMDisks_Task(). Thanks to my colleage Alan Renouf for the PowerCLI guidance.

This new feature should save you a lot of time when dealing with any future snapshot consolidation issues.

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About the Author

Cormac Hogan

Cormac Hogan is a Senior Staff Engineer in the Office of the CTO in the Storage and Availability Business Unit (SABU) at VMware. He has been with VMware since April 2005 and has previously held roles in VMware’s Technical Marketing and Technical Support organizations. He has written a number of storage related white papers and have given numerous presentations on storage best practices and vSphere storage features. He is also the co-author of the “Essential Virtual SAN” book published by VMware Press.