Posts Tagged ‘snapshots’

VMware Snapshot Alerting and Reporting

June 21st, 2010

I spotted an issue in my vSphere infrastructure this weekend just past. I noticed that one of the main development boxes was showing the dreaded question, redo log out of space, retry or abort?


As it turned out VMware Data Recovery Manager had taken a snapshot as part of it’s back up routine and had failed when trying to remove it.  This coupled with a scheduled SQL maintenance plan caused the delta files for the snapshot to grow to over 250GB in little over 12 hours.

I eventually overcame the issue by adding an extent to the out of space VMFS datastore, this gave me an extra 160GB with which to play the logs back in.  I then used the very handy SnapVMX utility to tell me how much space was required to replay the delta files.  Luckily for me it only required 20 GB as sometimes it can require as much as the size of the original disk. After the snapshot was merged I did a bit of Storage vMotion and reworked the datastore to get rid of the extent (I’m not a fan of using them)

This particular incident was unfortunately unavoidable, it happened at a weekend, was due to VMDR’s failure to remove a snapshot it had created and unfortunately clashed with a disk intensive operation. It did get me thinking though, although I am careful with snapshots and there usage who else in the organisation is not? how do we mitigate this potential risk?

Snapshots are a handy feature, I generally only use them for short periods of time, usually to provide a rollback when patching or changing configurations. Misuse or mismanagement of snapshots can quite quickly lead to problems, something that a recent blog article from VMware Support deals with quite effectively. Entitled ESX Anatomy 101 it’s a must read for anyone trying to gain a good basic understanding of how VMware snapshot work.

I myself have taken a two pronged attack to preventing snapshots causing problems. The first approach is to schedule a very basic PowerShell script that I found on the blog site of Axiom Dynamics.  This simple little script queries your vCenter server for all current snapshots and then sends an email detailing them.  A simple but effective means of keeping an eye on snapshots across the virtual infrastructure.

The second more proactive approach is to use a vCenter alarm at the data centre level to alert when a VM is running from a snapshot. This alarm simply involves emailing a warning when any snapshot is larger than 2GB. This handy video taken from VMware Knowledgebase article 1018029 describes in detail how to set this up, the KB itself also provides step by step instructions.


There are a number of alternatives available for reporting on snapshots.

Alan Renouf’s Snapshot Reminder – A Powershell script that integrates with AD to send the creator of a snapshot a little reminder when the snapshot is over 2 weeks old.

Alan Renouf’s vCheck Daily Report – Another Powershell script that reports on a large number of areas within the virtual infrastructure.  One of those areas includes snapshots

RVTools – A very handy .Net application by Rob de Veij  that can be used to query your virtual infrastructure for just about everything. You will notice in the screenshot below the vSnapshot tab which should help you identify those rogue snapshots.


In summary,  everyone who works with snapshots should have an understanding of their usage and limitations.  Obviously you can’t always rely on people to do things right, we are only human after all. As a safeguard ensure you have some level of reporting and alerting in place to help you prevent those annoying and time consuming out of space issues occurring.

VI Toolkit / Powershell, VMware , , ,

SNAPVMX – View your Snapshots at VMFS/virtual disk level

June 9th, 2010

Following a recent implementation of VMware Data Recovery manager we ran into a few issues.  We eventually had to kill the virtual appliances due to the issue we were having and as a result we had a couple of virtual machines with outstanding snapshots.  These snapshots were taken by VDR and as a result could not be viewed or deleted using the snapshot manager.

We raised a call with VMware support and they started a WebEx session to look at the issue.  I always love watching VMware support personnel operating at the service console level, I always pick up a command or two that I didn’t know before.  On this occasion the support engineer was using something called SnapVMX to view the hierarchy of snapshots at the virtual disk level.

At first I thought this was an inbuilt VMware command but it turns out it’s not. It was actually a little piece of code that was written by Ruben Garcia.  What does it do?  well the following extract from the download pages explains it pretty well.

  • Displays snapshots structure and size of snapshots for every disk on that VM
  • Calculates free space needed to commit snapshots for the worst case scenario
  • Checks the CID chain of the analysed files and displays a warning if broken.

I’ve included a little demo screenshot to show what it can do. On the left hand side is  a screenshot from Snapshot Manager within vCenter.  On the right hand side is the same VM being viewed with SnapVMX in the service console.  Put the two together and you get a better idea of the snapshot disk hierarchy and the size of each snapshot.


The other interesting feature is that it tells you what space is required to commit the snapshots.  So for example, say you had taken 5 snapshots of a machine as it was being built and configured.  Say that the overall effect of those 5 snapshots is to fill up your VMFS datastore completely. Chances are that you’re not going to be able to commit the snapshots within the current VMFS datastore.  SnapVMX will be able to tell you the worse case scenario on how much space would be required to commit the snapshots.  Armed with this information you could cold migrate to another datastore that has at least that amount of free space in order to allow you to commit the snapshots.  The screenshot below isn’t the best but the best I could do due to the length of the statement.


For the download and full documentation on how to use this piece of code head over to the following web site. Worth a look if you’re a big user of snapshots.

While searching for a link to Ruben Garcia to put on this article I found that he has a blog site and within that I found a link to a superb troubleshooting VM snapshot problems article which I will definitely be keeping a link to and suggest you check out.  Truly excellent stuff Ruben!

General, Gestalt-IT, VMware , , , ,

VI Toolkit & Powershell

September 24th, 2008

I’ve been meaning to look at Powershell for sometime now,  they’re always showing it off at Microsoft roadshows!!  So when I saw that Vmware had release the VIToolkit I thought now would be the perfect time to finally do something about it.

I’ve not been dissapointed,  I’ve been highly impressed by some of the entries in the VI Scripting contest and have been looking through and trying out some of the entries. You can find all the entries at the link below and the second link is the VI toolkit blog which is a great source of info and also includes the results from the competiton.

One of the ones that I have used and got immediate benefit from is Chris Uys snapshot finding script.  Imagine my horror when It reported it had found a 153Gb snapshot on a test database server from April this year. It was swiftly deleted and the script is one I will be using on a regular basis to ensure we’re managing the snapshots correctly.  You can find the link to the script below.

VI Toolkit / Powershell , , , , ,