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Managing VM snapshot retention policies using the VMware Event Broker Appliance (VEBA)

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vSphere Snapshots is an amazing technology that has enabled our customers to do so many amazing things from application lifecycle and testing to operating system updates and many other use cases. Like any technology, if it is miss-used, the benefits can quickly turn into challenge or nightmare.

As Peter Parker once said, "With great power comes great responsibility" which I think is one way to summarize VM snapshot usage 😆


I am pretty sure that every VI Admin out there has at least one story about vSphere snapshots gone wrong. Due to the convenience, ease of use and some times miss-understanding of how vSphere snapshot works, it can lead to a number of issues including filling up your storage and impacting other running workloads.

Now, imagine if you could implement a snapshot retention policy for your VM(s) based on the size of a given snapshot or maybe the number of days the snapshot has existed? Would that not be cool!?

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New Parameter in vim-cmd snapshot.remove for ESX(i) 4.1 Update 2

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While going through my ghettoVCB backlog this past weekend, I came across an issue reported by a user with snapshot removal using vim-cmd in ghettoVCB. It looks like with the recent release of ESX(i) 4.1 Update 2, the "snapshot.remove" required parameters have changed. Prior to 4.1 Update 2, the command would just require a virtual machine's vmid and if it only had a single snapshot, it would automatically consolidate the snapshot.

If a VM had more than one snapshot, users would then need to specify some additional parameters that identified the particular level of the snapshot tree and the snapshot index to be removed. This was pretty difficult to use, even for myself. It now looks like VMware has simplified this command and introduced a new required parameter called snapshotId in ESX(i) 4.1 Update 2.

Here's an example VM with several snapshots and let's say we would like to consolidate snapshot3

First we'll need to query the VM snapshots using vim-cmd vmsvc/snapshot.get [vmid]

As you can see from the screenshot, there is a new property called "Snapshot Id" which can now be passed into the snapshot.remove operation.

After the snapshot3 is consolidated, the snapshot tree is re-displayed again to verify the operation. We can also confirm by looking at the vSphere Client UI

This now makes snapshot manipulation using vim-cmd extremely easy to use.

There is a fix in ghettoVCB.next that will support the new snapshot.remove operation which hopefully I'll be able to release very soon.

How to control maximum number of VMware snapshots

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There are currently no methods of controlling the number of VMware snapshots using vCenter or ESX(i) permissions today, you either provide the snapshot privilege or you deny it all together. I recently discovered an undocumented .vmx entry that allows you to control the maximum number of VMware snapshots for a given virtual machine. By default, a virtual machine can have a snapshot tree depth of 31, in the worse case scenario supporting up to a maximum of 496 snapshots.

Here is what a VM looks like with 496 snapshots (unexpanded):

 

Note: If you are interested in what this looks like fully expanded, take a look at the screenshot at the very bottom of this post.

If you like to prevent the above or at least control the maximum number of snapshots for a given virtual machine, you can add the following into a VM's .vmx configuration file. Ideally, this is deployed using vSphere API as there is no need to directly edit the VMX's file and this can also be applied to a live running VM (another benefit of using the vSphere API).

Here is an example using PowerCLI:

$vm = Get-VM -Name TestVM
New-AdvancedSetting -Name snapshot.maxSnapshots -Value 1 -Entity $vm

For those that prefer using another vSphere SDK, you just need to use the ReconfigVM_Task() to add the VM Advanced Setting. Please take a look at this sample for here for how to add/update VM Advanced Settings.

snapshot.maxSnapshots = "n"

where n = max number of snapshots and n <= 496

Here is a screenshot of adding this .vmx parameter using the vSphere Client:

The virtual machine above already has one snapshot and per the configuration change, we should not be able to take any additional snapshots:

Next, we will try to take a second snapshot:

As you can see, an error is thrown that we have reached the maximum number of permitted snapshots. If you would like to disable snapshots all together, you can set the value to be 0 and this will prevent anyone from taking snapshots, including administrators.

Here is a an screenshot of the expanded view of a VM with 496 snapshots:

Note: These snapshots were created with a VM running in an vESXi host and script to exhaust the maximum snapshot depth of 31. Each snapshot level was also exhausted with the maximum number of snapshots. Starting from level-1: it was the maximum depth minus 1, level-2: it was maximum depth minus 2, and so fourth. This was just a test to see what the system could handle, you should not try this a home or on a production VM 😉 Use at your own risk