Because of its ease of deployment and integration, server virtualization can be a highly effective tool for disaster recovery. Server virtualization addresses three concerns related to disaster recovery:
- Cost: Virtualization allows companies to reduce the number of physical servers they deploy at production and recovery sites.
- Procurement delays: Virtualization eliminates most hardware dependencies.
- Rapid recovery: Virtualized server images can be rapidly deployed and in some cases, moved across physical systems.
When considering server virtualization in a disaster recovery strategy, storage administrators must take into account their data protection, recovery granularity and restore objectives.
Data protection (backups)
One challenging aspect of server virtualization and disaster recovery is that without valid and usable backup data, there is not much to recover. Virtualization alone does not ensure recoverability of the data. Several options are available for backing up virtual servers, and the results of each will vary. If a conventional backup agent is installed on each virtual machine, you can expect to get results comparable to those in a physical server environment.
If image-level backups (VMDK) are preferred over conventional backup agents because of the software cost reduction benefits, the backup strategy must be designed to be non-disruptive and to provide granular (file-level) restore capabilities. Third party software tools, such as vConvert from Vizioncore Inc. and PlateSpin Forge, help automate full and incremental image backups without taking the virtual server offline. This capability also allows for file-level restores.
One thing to keep in mind when backing up and restoring virtual servers is I/O performance. Virtualization is appealing because it allows the consolidation of otherwise under-utilized server resources. Although this holds true for many systems during production hours, it is often not the case during backups or, more specifically, during restores. The I/O generated by the simultaneous restore of 10 virtual servers on one physical system in a disaster recovery situation can become a serious bottleneck. Simply having hardware available does not guarantee that recovery time objectives (RTOs) will be met.
For applications with little to no tolerance for downtime (RTO=0), virtualization alone may not be enough; a failover component may need to be added to meet the recovery requirements. Likewise, for applications with stringent recover point objectives (RPOs) and little to no tolerance for data loss, a replication solution might be required to ensure data protection between scheduled backups.
However, all the virtualization, image backups and data replication in the world will not be much of a disaster recovery strategy unless there is an off-site component. A typical scenario includes virtual servers deployed or ready to be deployed at an alternate site with backups sent offsite or data replicated between sites.
About the author: Pierre Dorion is the Data Center Practice Director and a Senior Consultant with Long View Systems Inc. in Phoenix, AZ, specializing in the areas of business continuity and disaster recovery planning services, and corporate data protection.
This was first published in March 2008