Backup Restore and Recovery Considerations in Virtual Environments

Apr 2011

Backup Restore and Recovery Considerations in Virtual Environments

Posted by Scott Lakso in Cloud Backup

It is no secret that large and small businesses alike, are rapidly adopting server virtualization in their data centers and most indications are that this trend will continue.  When architecting virtual infrastructures, one of the first issues that business face is “What should I do for backup and recovery in a virtual environment?”

The most common approach, at least when starting out, is to ignore the fact that servers are now running on Virtual Machines (VMs) and backup the servers through the guest Operating Systems (Oss) just like you do when the OS is running on a physical server.  While this approach will work, it does have some drawbacks.  This approach typically requires you to load a backup agent on the guest OS in order to backup that server.  If the server is running an application such as Exchange, SQL or SharePoint, then you need to load a separate agent for each application.  Some backup applications also require separate agents to backup the Windows System State or Services Data Base.

When you load backup agents on a physical server, these agents are processes running on the OS, which require CPU resources.  Depending upon the agents, each agent might use less than 1% of the CPU resources or more than 15%.   Regardless of the resources required by the agents, this CPU overhead usually goes unnoticed on a physical server.

However, in a virtual environment, you could easily have 10 VMs running on a single physical host.  Each VM might have several agents on the server to accommodate backing up the file system, services database and applications.   Assuming a very conservative average of two agents per VM (each using 1% of the host’s CPU cycles), in a virtual environment, you would be wasting 20% of your available CPU resources on backup agents that don’t do anything during normal business hours. 

Once businesses realize the overhead in terms of wasted CPU resources, as well as man-hours required to manage all those agents, they typically look for a solution that will allow them to back up their VMs from the physical host side.  VMWare has the largest server virtualization market share so most of the major backup applications now support backing up VMs from the VMWare host side. 

Backing up VMs from the host side has advantages over backing up servers from the guest OS side.  First, there is no need to load or manage agents on each of the guest OSs.  This saves on both CPU resources and management overhead.

The next advantage is that it is typically much faster to backup and restore VMs from the host side, since you are backing up and restoring a single large VMDK file rather than backing up and restoring thousands of small individual OS, application and data files.   In a Disaster Recovery (DR) situation, where a VM’s OS becomes corrupted and you need to restore from a backup, it is very easy to point and click, and restore that system to another VM.  The disadvantage with many backup applications is they don’t support individual file restores.  If an end user deletes a single file, you need to restore the entire VM, find the file and give it to the end user, then delete the VM. 

When moving to a virtual infrastructure, it is a good time to evaluate your current backup application and to see if it meets all your needs.  If you determine that you need to invest in a new backup solution, you will want to choose one that will meet all your needs, now and in the future.  You should look for a solution that will allow you to restore the entire VM in a DR situation or to restore applications and databases like Exchange and SQL without having to restore the entire VM.  You should also consider a solution that allows you to restore individual Exchange messages or individual SharePoint items, without having to restore the entire database.

Finally, you should seriously consider a backup recovery solution that supports both physical servers and virtual environments. And the BUR solution should support more than just VMware.   While VMware may have the lion’s share of the virtualization market share today, they are starting to face significant competition from other sources such as MS Hyper-V, XenServer and Parallels to name a few.  Whenever a technology vendor thinks that a customer has no alternatives and is locked into their solution, they have very little incentive to reduce the cost of their solution.  Bringing in an alternative virtualization solution may provide VMware an incentive to reduce their price.  But you shouldn’t have to invest time and money in a new backup solution just because you want to try an alternative to VMware.

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