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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

Where are the "Power" Perf Metrics in the vSphere API?

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A recent question was posed on the VMTN developer forum on how to obtain the new power utilization metrics using the vSphere API. This new performance metric was introduced with the release of vSphere 4.x and can be seen using either esxtop or resxtop and specifying the "p" option for power if you are on an ESX or ESXi host.

You can also get these counters by using the vSphere Client and using the Advanced Charts:

This actually seemed like a simple enough question, pointing the user over to the vSphere API reference documentation under the perfManager. Though after taking a second look, it appears that no such metric exists in the documentation from VMware:

After a few minutes of digging around, I found that Power metrics actually do in fact exists but were not properly documented when they were first introduced. I wrote a quick vSphere SDK for Perl script called perfQuery.pl looking for metrics that were related to "power" and I identified the following:

As you can see these match up to those seen using the vSphere Client and I output the metrics using its rollup type, units, internal name and metric description. While writing this script, I also noticed there were two other performance metric types that existed and were not documented by VMware. Here is a mapping of the API performance metric keys to vSphere API perfManager, the last two including power metric types are undocumented by VMware:

vSphere Client Chart Option vSphere API Perf Metric Key Documented
Cluster Services clusterServices yes
CPU cpu yes
Management Agent managementAgent yes
Memory mem yes
Network net yes
Resource Scheduler rescpu yes
Storage Capacity disk yes
Datastore datastore yes
Disk disk yes
Virtual Disk virtualDisk yes
Storage Adapter storageAdapter yes
Storage Path storagePath yes
System sys yes
Virtual Machine Operations vmop yes
Power power no
vCenter Resources vcResources no
vCenter Debug Info vcDebugInfo no

Using the script and the performance metric key, you can actually query either all or a specific metric type that you are interested in. This is helpful, for those metrics that have not been publicly documented by VMware. However, the power metric should have been documented and I believe this to be a documentation bug that was missed by VMware.

Download: perfQuery.pl

If you are interested in learning more about the vSphere statistics and performance monitoring, I highly recommend checking out Luc Dekens three part series (Part1, Part2 and Part3) on vSphere performance monitoring. Even though his posts are specific to PowerCLI, all the concepts discussed apply to all the vSphere SDKs when dealing with performance monitoring using the vSphere APIs.

vGhetto Tech Exchange VMworld 2010 Video

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Back in September, I presented at my very first VMworld: vGhetto - Communities Building Great Solutions (PPC-07) alongside Edward Haletky at Tech Exchange VMworld 2010. For those that missed the session, the famous Pablo Roesch of VMware has graciously uploaded our presentation to Vimeo 🙂

You can view the presentation here.

vGhetto - Communities Building Great Solutions from heyitspablo on Vimeo.