- What Do You Do With Your Swap File? – VMworld Update, Thursday
Your VM’s Swap File that is… The inspiration for this post came from a conversation I had with a customer in the backup and recovery booth here at VMworld 2012. This particular customer was asking if EMC’s Avamar had any sort of intelligent means of isolating swap files from the GUEST OS when doing a VM image backup.
So the answer to this question? Not Yet. But, Stay Tuned!
From a technical perspective it’s actually not as trivial as you might think. Complications arise when having to account for all permutations and flavors of OS versions and how they handle paging. So, handling this in an automated fashion while assuring essential user data doesn’t get left out is no easy task.
However, using another Avamar feature in combination with configuring your VMs in a certain way, you can avoid backing up unnecessary data residing in VM swap files. The approach to this solution would be to configure your VMs to store this data on an entirely separate virtualized disk or VMDK. In fact, you may already have your VMs configured this way for reasons such as guest performance, or “replication traffic reduction” for Site Recovery Manager (SRM) implementations. In the SRM instance, for example, placing swap file data in a non-replicated data store can greatly reduce the amount of unnecessary data you are replicating across your “mucho dinero” WAN to your DR site.
For backup, taking advantage of this concept can also save you from dealing with essentially random “dedupe-clogging” page file data. Using the isolation concept for swap files in separate VMDKs, one can leverage Avamar’s disk level granularity feature as highlighted in the graphic above to essentially skip scanning and backing up the guest OS swap file data. When specifying VM backup policies, the administrator has the ability to select specific VMDKs associated with a particular VM that is being targeted for backup. It’s as simple as just leaving out the VMDKs that contain the swap files. Based on some customer environments, and in particular this customer’s implementation, the savings of backup capacity by following this practice is enough to warrant thinking about it.
I had some great conversations with customers at this conference and am truly excited about the continued innovation and fundamental technological shift we are experiencing in our daily computing lives. Feel free to comment on this blog post and chime in with ideas on how you are handling Guest OS swap files. In the mean time, bring on the next trade show!