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Disaster recovery methods for virtual servers

Companies protect their virtual servers from disasters with several different methods such as traditional backup and recovery, synchronous or asynchronous replication, or CDP.

Different companies require different disaster recovery methods for their virtual servers. Depending on the hypervisor...

in use, IT infrastructure in place, and expected recovery time objective (RTO) and recovery point objective (RPO), companies choose to protect their virtual servers using traditional backup and recovery methods, synchronous or asynchronous replication, or continuous data protection.

Traditional data backup and recovery

Small- to midsized businesses (SMBs) with a small number of virtual servers frequently back up their virtual machines (VMs) and restore them in the disaster recovery site in case of a disaster. Because the restore can be done on almost any hardware that runs the hypervisor software, hardware requirements for restoring physical servers are not an issue. Being able to restore multiple VMs to a single host further reduces hardware requirements for the secondary site and significantly lowers the overall cost of DR.

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In its simplest form, virtual servers can be backed up by installing backup agents in the virtual machines, but that adds overhead and will likely impact server performance while backups are running. Companies that run VMware have the option to deploy VMware's Consolidated Backup (VCB), which removes the backup load from virtual machines. Besides backing up each VM, backups can be taken at the hypervisor level, eliminating the need to install agents on each virtual machine. However, the disadvantage is that it only allows restoring at the virtual machine level.

Backup software vendors like CommVault have extended their backup suites to accommodate the backup needs of virtual servers. The majority of data 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," said Peter Kovaleski, network Unix administrator at Oral Roberts University in Tulsa, Okla. "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 virtual machine 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 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," said Peter Allen, director of IT operations at Nixon Peabody LLP in Rochester, N.Y., an international law firm.

Continuous data protection

Continuous data protection products such as Double-Take for Virtual Systems, FalconStor Software Inc.'s CDP Virtual Appliance for VMware Infrastructure and Network Storage Server and InMage Systems Inc.'s DR-Scout are viable disaster recovery alternatives to storage-based snapshots and replication. They're less expensive, especially for customers who don't have matching storage systems in the primary and secondary data center. Also, changes are captured and replicated as they occur, so they add very little overhead to VMs. Finally, continuous data protection 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," said Jim Yarber, senior manager of network operations at Heritage Bank of the South in Albany, Ga. "I have a 100 Mb 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 disaster recovery to a larger number of servers and applications.

This article originally appeared in Storage magazine.

About this author:
Jacob Gsoedl is a frequent contributor to
Storage magazine.

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