Introduction:
There is a potential for data loss if VMware virtual machines protected by Backup Exec for VMware option have the block level incremental backup feature enabled in the backup policy and non-Backup Exec initiated snapshots are reverted in the time period between backups.

This issue is not caused by Backup Exec or NetBackup.  

This article provides you with details for the Backup Exec product.  For NetBackup information, refer to the Related Documents section of this article.


What is affected:
Backup Exec 2010 clients running the Agent for VMWare Virtual Infrastructure (AVVI).


How to determine if affected:
Data loss may occur if ALL of the following conditions are true:

This is a limitation in VMware Change Block Tracking (CBT) framework. Reverting to a pre-existing snapshot can cause incremental backups based on CBT to become inconsistent.  All products capable of using CBT are affected. Please see the details published by VMware:
 http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1021607


Workaround:
If it is necessary to revert a manual snapshot of the virtual machine, the next backup for that virtual machine must be a full backup. A full backup can be manually initiated from the Backup Exec's Administration Console.  
     
Note: In environments where vSphere and Backup Exec are managed by different administrators, Symantec strongly recommends forwarding this alert to vSphere administrators as well.  Please advise the vSphere administrators/power users to notify Backup Exec administrators if snapshot reversions are planned for production virtual machines, as the next backup for the virtual machine should be forced to be a full backup.

Formal Resolution:
Because this is not a Backup Exec issue, there are no plans to address this issue in a future Backup Exec version.  Symantec strongly recommends implementing the Workaround listed in this article.

Best Practices:
Symantec strongly recommends the following best practices:

1. Always perform a full backup prior to and after any changes to your environment.

2. Always make sure that your environment is running the latest version and patch level.

3. Perform periodic "test" restores.

4. Subscribe to technical articles.  

How to Subscribe to Email Notification:
Article Subscription: Subscribe to this TechNote for any updates that are made to this article, by clicking on the following link:    http://maillist.entsupport.symantec.com/notification.asp?doc=355664

Software Alerts: If you have not received this from the Symantec Technical Support Email Notification Service, please click on the following link to subscribe to future Notifications:        http://maillist.entsupport.symantec.com/subscribe.asp