Many organizations have virtualized their test, development, and low-duty-cycle application servers, freeing up rack space and reducing the power and cooling load in the data center. Now, as these organizations get ready to virtualize the servers that hold their most vital, high-traffic data, they're wondering: "How do we back these things up?"
There are a couple of paths that lead to easy, reliable virtual server backups, from the obvious to the innovative. Administrators can conduct image backups that make total system backups and restores fast and relatively painless--but they must be repeated often to keep up with virtual system changes. The alternative, agent-based backups on each host, provides file cataloging and indexing, direct backup and restore from tape, and individual item restore from databases like Exchange--but requires significant system resources and careful management to avoid agent sprawl.
While weighing the pros and cons of each approach, administrators also have to choose their server virtualization backup tools. Like server virtualization platforms themselves, virtual machine backup software is evolving rapidly. Vendors are working to provide the same level of consistency and granularity regardless of whether VMs are backed up via host agents, guest agents, or a centralized proxy like VMware's Consolidated Backup. Linux and Solaris file-level restores are also on the virtual menu.
Still, there's no one best backup tool for virtual servers. New software designed specifically for virtual systems might be a good choice for backing up servers that need full data restoration more than partial restores; tried-and-true workhorse tools may be better when data needs to be stored for more than a few days.
The most obvious way to back up a virtualized server is to install an agent for your existing system on each virtual server and use the same procedures you use now. Backing up virtual servers with locally installed agents has its advantages, not the least of which is familiarity. Using local agents generally provides the most granular backups and is the only way to restore individual items from databases, such as message-level restores.
However, using an agent on each virtual server can create a substantial load on the host CPU and network connections, not to mention the cost and effort associated with installing and maintaining all those agents. Also, because the agent runs in the virtual machine, this technique can't back up VMs that are shut down.