Should I Remove My VMware Snapshot?

Yes…the answer is yes.  VMware snapshots can be a very helpful tool when making any kind of changes to your environment.  However, if not properly managed they can cause a lot of issues.  Downtime, corrupted virtual machines, and data loss are just a few of the problems that can occur by forgetting to delete a manual VMware snapshot.

There are several reasons why you would want to take a snapshot of your virtual machine.  Applying Windows Updates, installing a new application, or updating an existing one are all excellent examples of instances where it’s great to have a snapshot as a safety net.  However, it is extremely important to remove that snapshot after you verify that everything is working properly.

In order to understand why the snapshot must be deleted, it might help to explain exactly what happens when you take a snapshot.  Prior to making a major change to a particular virtual machine, one can take a snapshot.  A snapshot is a copy of the virtual machine disk file (or VMDK) at a given point in time.  Snapshots create a change log for the virtual disk and can be used to restore a VM to a particular point in time in case of failure or system errors.

For example, say you have a SQL server to which you would like to apply the latest service pack.  Before installing the service pack, you can take a snapshot.  If the installation fails or the system becomes corrupted, you can revert back to the snapshot and the server returns to its original working state.  If the installation completes successfully, continue to test server functionality.  If everything is working properly, simply delete the snapshot.

If you forget to delete the snapshot, the change log file that is created at the time of the snapshot will continue to grow and grow.  Depending on the rate of data change, the file can become quite large in a short period of time.  Exchange and SQL servers have a very high rate of data change, possibly yielding snapshot files gigabytes in size within days.  Since the snapshot file resides on the same datastore as the VM, this could eventually cause the datastore to run out of space.  Once the datastore runs out of space, all of the virtual machines on that datastore become inaccessible and will not power on until either clearing enough free space or by increasing the size of the datastore.  This can sometimes be a time consuming process, not to mention the risk of data corruption.

If you take a snapshot, always remember to delete it when you’re done with it and it will be smooth sailing!

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