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Because storage admins are most familiar with the use of agent-based backups, analysts suggest adoption of a multilayered approach to data protection, one that combines agent-based backup with consolidated or serverless backup and snapshot or cloning technology.
Another method of VM backup is the use of a proxy server. Sometimes called serverless or consolidated backup technology, the introduction of a proxy server into the environment can reduce overhead and increase performance. Backup processing is offloaded from the host computer being backed up to this consolidated backup server.
The most commonly used software of this type is VMware Inc.'s Consolidated Backup (VCB). In VCB, a series of drivers and preconfigured scripts execute the backup. A script takes a snapshot of the VM and mounts it to the proxy server. The script then quiesces the file system within the VM, while the backup software agent creates a virtual disk image of the VM. The mount is then destroyed and the virtual disk is removed from snapshot mode. Snapshot and cloning are also included in software from VMware and Citrix Systems Inc.'s XenServer Enterprise Edition (formerly XenSource XenEnterprise), as well as in many backup software packages.
Many backup vendors, including CommVault, EMC and Symantec, have recently announced the capability of their software to work with VCB. Carmine Iannace, director of IT at
| the Cambridge, MA-based Brattle Group Inc., has taken a combination approach to backing up his 75 virtual machines. "We install CommVault Simpana backup agents directly into the virtual guests and back them up and restore them just as if they were a physical server," says Iannace. For server failover and redundancy, Iannace uses a product from Neverfail Ltd.
"With Neverfail, if the email system malfunctions or if the site goes down in Cambridge, MA, we could resume our email functionality from Washington, DC, for the entire firm," says Iannace.
Bare-metal restoration of Iannace's VMs is also handled by CommVault Simpana. "From a physical host perspective, the VMware hosts are quite easy to recover," says Iannace. "We can easily restore those and recover the virtual guests. That's not considered a big roadblock for us."
Jim Klein, director of information services and technology at the Saugus Union School District in Saugus, CA, has also taken a combined approach. "We treat the virtual machines just as if they are physical servers with backup agents and software from the open-source software Bacula," he says.
Because images of VMs are standardized and stored on Klein's SAN, for bare-metal recovery, "we just basically recreate machines on the fly and then restore the data to it. It reduces the amount of backup tape that we need and increases our efficiency." Klein also uses a proxy server to offload processing from his host computers.
This was first published in February 2008