Virtualization facilitates storage flexibility and nondisruptive migration. However, virtual storage is not an...
essential element of virtual disaster recovery (DR). The DR site will require enough total disk capacity to hold storage volumes migrated from the primary site, but that storage does not need to be virtualized. Servers must have local storage large enough to retain all of the virtual machine (VM) images intended for that physical system, so the DR servers and their local storage are almost always virtualized.
Properly utilizing storage in a virtual environment can improve DR. Pierre Dorion, data center practice director at Long View Systems Inc., an IT solutions and services company headquartered in Denver, points out that disk failure can cripple a physical DR server and leave numerous virtual machines inaccessible. It's critical to protect VMs at the DR site with more traditional backups like tape.
A virtualized DR site is best served with a storage area network (SAN). The centralized high-performance storage that a SAN provides adds redundancy instead of relying on individual disks within physical servers to do so. It also enables rapid migration of virtual images between systems.
"Virtualizing servers does not guarantee reliability," Dorion said. "You still need to make sure that your data is adequately protected."
Consider alternatively storing VM images on protected disk storage, such as RAID, in SANs or in NAS arrays. Centralizing VM image storage also allows more efficient reallocation from one physical server to another.
Cost-conscious organizations may be reluctant to fund a conventional Fibre Channel SAN for a remote DR site. Instead, they can consider an iSCSI SAN deployment to support storage and IP traffic on the same network. For many organizations, iSCSI running on a 1 GB Ethernet network strikes an acceptable balance between affordability and performance.
What DR storage tools are out there?
Software tools are critical for replicating VMs and storage volumes and most virtualization vendors offer DR tools. Citrix XenServer 5 has built-in live migration and DR features. Other vendors, like VMware Inc., have separate complementary tools; VMware Consolidated Backup is designed to protect an entire VMware environment under VMware Infrastructure 3. VMware VMotion can move VMs nondisruptively between physical servers. And Windows Server 2008 R2 includes live migration of VMs between servers.
Server clustering software can also play a role in a virtualized data center or DR environment; Veritas Cluster Server from Symantec Corp. is one example. Clustering enables physical servers to work in conjunction with each other, sharing collective computing resources to handle more workloads or improve performance. Clustering also supports high availability (HA). If one physical server fails, remaining cluster elements take control and continue processing.
Other third-party software, such as vFoglight from Vizioncore Inc., can further enhance a virtualized environment by monitoring VM performance. Vizioncore's vReplicator enhances DR and HA within a VMware environment.
Stephen J. Bigelow, Senior Technology Writer, can be contacted at firstname.lastname@example.org.