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VM backup strategies
D'Costa identifies three main approaches to backing up virtualized servers: conventional server backup with the use of individual backup agents on each VM; use of the backup management tools provided by the virtualization vendor; and the use of a standalone backup proxy server, such as VCB, or appliances from third-party vendors.
A storage manager might be tempted to simply back up the VMs on the physical host like regular files. In this case, the organization would back up each VM's VMDK, a large disk file containing the VM configuration and data. Nice idea, but it might not work well. Unless the VM is shut down, you might back up data in use, which is likely to result in inconsistent data.
The use of an individual backup agent on each VM can avoid data inconsistency by quiescing the app during backup. However, this approach can result in high backup software licensing fees if the organization must purchase an instance of the license for each VM. It also creates a potential for resource contention unless the organization staggers its virtual backups. Still, the advantages of putting
| a backup agent on each VM are simplicity and familiarity. The backup procedure runs no differently and admins can do all of the usual things, such as file-level recovery, and full or incremental backups.
However, the backup application, unaware of the encapsulated nature of the VMDK files, can't do things it otherwise might do to speed backup, notes Mainland Information Systems' D'Costa. This approach also undermines some of the efficiencies organizations hoped for from server virtualization in the first place as each agent must be managed individually.
D'Costa's second approach runs the backup software in the virtualization server itself, such as VMware ESX. This will likely be a Linux backup agent capable of backing up all of the VMs. However, this results in image-level backups that, although fast, don't allow for the easy recovery of individual files. It also requires scripting to automate the shutdown, snapshot and restart of the VMs.
The proxy server (particularly VCB), D'Costa's third approach, may become the most popular. The proxy server moves the backup from agents on the VMs or from the virtualization server to a dedicated server. In the case of VMware, "you put the backup agent on VCB and back up all the VMs," says Server Centric Consulting's Miller.
The proxy server is typically a Windows server connected to the same SAN volumes as VMware's ESX server. "With VCB you can now back up multiple VMs on the same physical host and VCB organizes the backups to keep them from overusing the resources," adds Miller. VMware provides a load balancer called Distributed Resource Scheduler (DRS).
But VCB is far from a backup panacea. D'Costa points out that it requires a number of pieces to work right: a sync driver on the ESX server to flush the file systems and create a snapshot, a vLUN driver on the proxy server to present VMDKs to the proxy, and command line utilities to assist with scripting automation through the command line interface (CLI). It also will require an integration module provided by VMware or the backup application vendor.
Storage managers often mix different approaches. For example, Rockledge, FL-based Health First is a three-hospital healthcare provider network serving Brevard County. It uses VCB through a third-party tool, Vizioncore's vRanger Pro, to back up 1.5TB of data from approximately 220 VMs every night. The data is backed up to disk. However, the hospital also uses IBM Tivoli Storage Manager (TSM) and installs a TSM backup agent on some of the VMs. The TSM backups go to disk and then to tape, which is shipped offsite.
VCB and vRanger Pro let the team "deal with the growth of VM sprawl," says Joel Otero, network engineer at Health First. Some days "we're building 10 to 15 VMs. Tivoli couldn't keep up with that. It's far too much to script," he explains.
W.R. Berkley combines VCB with Veritas NetBackup and FalconStor Software Inc.'s Network Storage Server for backup and recovery of its virtualized Windows and pSeries servers. The FalconStor product takes snapshots a few times a day and replicates them to a second data center. "So we risk, at worst, losing a couple of hours of data," says W.R. Berkley's Whelans. Using VCB, the company can restore individual files. FalconStor also spins off the snapshots to tape every night.
This was first published in September 2008