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Hot Spots: VMware opens door for next-gen backup apps

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The special .vmdk files that store each virtual machine can't be targeted directly for backup without first quiescing the virtual machine image. When the virtual machine is running, the disk file is open and being written to by the virtual machine. Powering off the virtual machine for backup makes it safe to back up the .vmdk file; however, the virtual machine is suspended, as are all activities in the virtual machine. As an alternative to powering down, ESX Server includes the vcbMounter command line utility that creates a consistent snapshot of the virtual machine and exports the snapshot to files that any backup solution can target for backup.

There are two ways to back up virtual systems: file-level and system-level backup/recovery. With file-level backup/recovery, the main concern is with the files within ESX Servers and the virtual machines, whereas system-level backup/recovery includes the entire ESX Server or virtual machine. With each approach, you must consider the recovery trade-offs.

With file-level backups, you get file-level restoration. Recovery of a single file is faster and easier than recovering from a system-level backup. System-level backups (i.e., backup of the .vmdk file and the .vmx configuration file) allow for a complete virtual machine restore similar to bare-metal recovery. Single file recovery from a system-level backup could involve a two-step restore: recovery to an alternate virtual machine and then recovery of the individual

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file.

Backup options and deduplication
There are many approaches that can be taken when backing up VMware environments:

Backup agent in each virtual machine. Backing up at the guest OS level (the equivalent of how backup is done in the "physical world") is simple and guarantees consistency. This method supports full and incremental backups, as well as application-specific backups. There are a few disadvantages:

  • This method lacks bare-metal recovery options, so a virtual machine can't be restored as a whole.
  • It's burdensome on the host's shared resources.
  • It's necessary to set up backup scheduling and policies for each virtual machine.
Client-based deduplication provides a possible answer to the burden placed on system resources. Because a full backup requires data to be read and pushed out to the backup engine, deduplicating data within a virtual machine and across virtual machines will significantly reduce the strain on shared resources and applications, as well as the amount of data copied and stored.

This was first published in September 2007

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