Server virtualization strategies for disaster recovery

Remote replication on virtual machines adds up to a disaster recovery plan that can really work.

Server virtualization offers considerable benefits for organizations that want to implement remote replication for disaster recovery (DR) purposes. This includes reducing recovery time objectives (RTOs), the costs associated with remote site server infrastructure and improving ease of implementation of remote DR. Research from Enterprise Strategy Group (ESG) finds that 26% of organizations are replicating virtual machine images to a remote disaster recovery site, and another 39% plan to do so in the future.

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Server virtualization runs multiple virtual machines on a single physical server for improved resource utilization and hardware consolidation. Improved business continuity and lower data center operating costs are additional benefits that are quickly becoming the primary drivers of server virtualization deployments. Today, the closest IT organizations can come to guaranteeing a service level for a specific application in a physical server environment is to deploy infrastructure and applications as dedicated silos that are isolated from any potential outside impact. However, this type of implementation leads to poor utilization and the likely purchase of additional hardware for high availability. But server virtualization can enable the sort of business resilience you need without the compromises that come with silos. When talking server virtualization and business continuity, there are a few key concepts to understand:

  • Hardware independence. Server virtualization provides a layer between the physical hardware and the operating system and applications, allowing virtual machines to run on any approved x86 hardware.
  • Isolation. Multiple virtual machines run in an isolated environment. If one virtual machine goes down, it doesn't affect others running on the same host. Multiple operating systems can run on one physical machine, improving hardware utilization. This creates a cost-effective means of establishing failover targets in disaster recovery strategies.
  • Encapsulation. Virtual machines are stored as hardware-independent files. Encapsulating the virtual machine into a single file enables mobility and allows multiple copies of the virtual machine to be created for DR purposes.

Combining server virtualization with business continuity solutions employed in physical environments, such as replication, enables a more cost-effective disaster recovery strategy. Replication provides a mirror copy of primary system data on a local or remote secondary system. If the primary system has an interruption of service, the secondary system can take over, minimizing downtime and data loss.

In a physical-to-virtual (P2V) configuration, a production application running on a physical machine is replicated to a virtual machine running on a secondary system. A virtual-to-virtual (V2V) scenario has production and recovery applications running on virtual machines. A higher degree of synchronization is achieved because these machines periodically or continuously replicate over a LAN or WAN to a virtualized standby system. Due to this greater frequency of replication, data loss is minimized in the event of an outage.

A virtualized disaster recovery site

Consolidating physical servers at the disaster recovery site eliminates the need for one-to-one mirrored physical machines, and can deliver savings in power, cooling, management and maintenance. The portability of virtual machines also means that failback can occur to the original location or to a new one: either a virtual machine or a physical system with dissimilar hardware.

Another advantage is the ability to test disaster recovery more efficiently. Regular DR testing -- confirming failover and failback processes, and testing documentation -- is necessary when preparing for disaster recovery. In server virtualization environments, disaster recovery tests can be performed on a virtual machine without affecting another machine or the primary production system. Tests can be run in more realistic situations (during peak hours, with peak-time staff and on actual DR hardware) without affecting normal operations and with less risk.

P2V- or V2V-based replication offers a big improvement over tape-based backup/recovery, especially when it comes to recovery point objectives (RPOs). With tape, an organization could lose up to a full day's data because tape backup usually occurs once per day. With replication, incremental changes are captured as they happen, and can then be replicated to one or more local or remote virtual machines. Tape-based backup is more affordable, but the recovery process is slower, more manual and error-prone. Replication also lets you effectively meet budget and recovery requirements.

More sophisticated clustering solutions take immediate action by starting up applications at the DR site and making them available to users. Clustering meets aggressive recovery objectives, but is often more complex and costly to implement and manage. Clustering solutions have moved into the virtual world and protect virtual machines in much the same way they protect physical machines.

With server virtualization, remote replication becomes cost-effective for organizations that haven't previously implemented disaster recovery, or for tiers of application servers that may not have justified aggressive RTO objectives, but would still be painful to manually recover.

This article originally appeared in Storage magazine.

About this author: Lauren Whitehouse is an analyst with Enterprise Strategy Group and covers data protection technologies. Lauren is a 20-plus-year veteran in the software industry, formerly serving in marketing and software development roles.


This was first published in July 2009

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