DR for virtualized servers


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Backup software vendors like CommVault have extended their backup suites to accommodate the backup needs of virtual servers. The majority of backup software vendors' products are integrated with VCB and some have added extra features. "We use VMware VCB and CommVault Galaxy to back up about 70 VMware ESX guests," says Peter Kovaleski, network Unix administrator at Oral Roberts University in Tulsa, OK. "The CommVault restore agent allows us to directly restore files back to ESX hosts, eliminating the manual copy process of files from the proxy server to the VM."

Synchronous or asynchronous replication: Storage system-based snapshots and replication are the prevailing methods in the enterprise space to get VM images and data from a primary to a secondary site. From a storage and replication perspective, the requirements to protect physical and virtual servers are very similar.

To start, snapshots are scheduled to capture all changes since the last snapshot. The frequency of snapshots varies and depends on the acceptable RPO. A key requirement during snapshots is quiescing virtual servers to ensure that the entire state of VMs is captured at the point the snapshots are created. Snapshots are then replicated to the secondary site via synchronous or asynchronous replication.

Among all hypervisors, Microsoft faces

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the fewest integration issues with storage systems because it uses NTFS and VSS, protocols that are widely supported by storage vendors. Similarly, because of its 70% market share, VMware enjoys widespread integration support, especially for its Site Recovery Manager, which is supported by most major storage vendors.

Storage system-based snapshots and replication are favored by enterprise customers because they're likely to already have storage systems with snapshot and replication support and are hesitant to sign up for less-proven alternatives like continuous data protection (CDP). "We decided to use NetApp and NetApp's SnapManager for Virtual Infrastructure because it allowed us to automate what was previously scripted, from quiescing the virtual machines and taking snapshots to replicating them to the secondary site," explains Nixon Peabody's Allen.

CDP: CDP products such as Double-Take for Virtual Systems; FalconStor Software Inc.'s CDP Virtual Appliance for VMware Infrastructure and Network Storage Server (which enables automated, application-consistent failover in geographically dispersed clusters of both physical and Hyper-V virtual servers); and InMage Systems Inc.'s DR-Scout are viable DR alternatives to storage-based snapshots and replication for several reasons. They're less expensive, especially for customers who don't have matching storage systems in the primary and secondary data center. Because changes are captured and replicated as they occur, they add very little overhead to VMs. Finally, CDP products not only provide for failing over to the latest replica, but allow users to easily roll back to previous points in time.

"We chose DR-Scout over array-based replication because of its minimal bandwidth use," says HeritageBank's Yarber. "I have a 100Mb Ethernet connection between our two data centers, and DR-Scout barely scratches it."

Without question, virtualized servers are revolutionizing disaster recovery. DR has always been expensive and many plans only cover mission-critical apps. A high level of mobility and the relative hardware independence of virtual servers greatly reduce the cost and complexity of putting disaster recovery in place, enabling companies to expand DR to a larger number of servers and applications.

This was first published in December 2008

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