Virtual servers put pressure on backup


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If you're doing VM backups that way and they're working, don't worry. The good thing about doing conventional backups is the simplicity of the process. Virtual machine backups work the same as "real" backups; you have access to file-level recovery, database and app agents, and incremental backups (see "Improving old-style virtual machine backups," below).

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Improving old-style virtual machine backups

You can do several things to improve backups of your virtual servers if you're using traditional software.

  • Make sure you're staggering your backups and definitely staggering your full backups.
  • Try decreasing the frequency of your full backups; go from weekly to monthly full backups. This is a no-brainer if you're going to disk.
  • Finally, consider synthetic full backups if your backup application supports them. Perform incremental backups in the virtual machine, but create your full backups synthetically inside your backup software. This feature is available in popular backup applications, including CommVault Simpana, EMC Corp. NetWorker and Symantec Corp. Veritas NetBackup.

Backup from inside ESX server

Another option is to run your backup software at the physical level inside the ESX server. But things get ugly quickly and you'll find yourself doing full backups every day. You're also likely to be doing this without any support from your backup software company, which has little incentive to make this method work. (They'd much rather you use VCB or even the typical agent approach as they get more revenue that way.) The reason you end up doing full backups every day is because any change in the VM results in a modification of the timestamp of its associated VMDK files. So even an "incremental" backup will be the same as a full. This is rarely the best approach to virtual server backup.

VMware Consolidated Backup: Hope or hype?

VMware's answer to the backup dilemma is VMware Consolidated Backup. To use VCB, you must install a physical Windows server next to your ESX server and give it access to the storage that you're using for your VMFS file systems. It can access both block-based (Fibre Channel and iSCSI) and NFS-based data stores. The server then acts as a proxy server to back up the data stores without the I/O having to go through the ESX server.

There are two general ways a backup application interacts with VMware Consolidated Backup. The first method only works for Windows-based VMs. With this method, the backup application tells VMware via the VCB interface that it wants to do a backup. VMware performs a Virtual Shadow Copy Service (VSS) snapshot on Windows virtual machines and then performs a VMware-level snapshot that's exported via VCB to the proxy server as a virtual drive letter. (The "C:" drive on the VM becomes the "H:" drive on the proxy server.) Your backup software can then perform standard full and incremental backups of that virtual drive.

This was first published in August 2009

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