What To Look For In Virtual Server Backup Products

Feb 20, 2009 (07:02 PM EST)

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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.

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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 Short List

  Agent On Guest OS Agent/ Backup Software On Host Consli- dated Backup
Atempo X X X
BakBone X X X
CommVault X X X
PHD Technologies     X
Symantec X X X
Veeam     X
Vizioncore     X

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.

Host-Level Backup

The other option is to back up virtual server hosts, and therefore guest VMs, through an agent installed in the host's operating system or the virtualization platform's service console. It makes sense: If you have 16 virtual servers running on each host, backing up the hosts rather than the individual guests, that will be one-sixteenth as many backup jobs to manage and one-sixteenth the number of agents to install and update.

Most basic backup applications take a snapshot of the logical drives that hold a VM's virtual disk and configuration files. Those snaps are then backed up as files in the host.

A host operating system backs up the VMs and their virtual drives as a set of files. However, VM volumes with direct mappings to SAN logical disks via iSCSI or Fibre Channel can't be backed up this way because they're not visible to the host operating system.

Most organizations start by consolidating physical servers to virtual ones, then use their hypervisor's live-motion features to move servers as user demand varies. However, with host-level backup, admins must modify backup schedules to account for every move a VM makes, or risk not backing up the migrated VM. In these cases, companies may need to install additional job manager/scheduler software that can keep track of hosts and the VMs on those hosts. Most virtual server backup vendors don't provide this capability.

The Scramble Is On

During the past couple of years, a wide range of software vendors has created backup apps that capitalize on VMware's built-in snapshot capability, either directly or via proxies to run scheduled disk-to-disk backups of VMs and their data.

For example, PHD Technologies esXpress and products like it create hot image backups of virtual machines through virtual backup appliance VMs on each VMware ESX host. Once the snapshot file is created, esXpress can compress and optionally encrypt the files, and save them to a VM file system, FTP, SSH, or CIFS server across the network.

The Essentials

  Pros Cons
Agent On Guest OS Same backup process as physical servers; high backup/restore granularity High load on host server; many agents to maintain
Agent/Backup Software On Host Fewer agents to maintain High load on reduced restore granularity
Conslidated Backupt Fast LAN-free backups, integration with existing backup apps Reduced restore granularity; requires scripting or software

PHD esXpress ranges from free to $1,995 per ESX host. The free edition is limited to two simultaneous backups at 13 Mbps each; other editions add features, performance, and more simultaneous backups.

Veeam Backup and Vizioncore vRanger Pro both perform disk-to-disk backups of VMware ESX servers, and both can ensure application-consistent backups for Windows VMs. VRanger is priced at $499 per ESX host processor with volume discounts.

Like comparable products, Veeam Backup performs a full backup the first time it encounters a VM and incremental backups thereafter. It's priced at $495 per ESX host processor.