Weekly quickTIP

Hooray for Transactional Integrity!

Image-level backup consolidates that server's state into one nice and tidy bundle.

• By Greg Shields
• 04/21/2008

Image-level backups are a great benefit gained when an IT environment moves to virtualization. These single-file backups allow the state of an entire server to be restored without all the thousand-file nastiness required in a traditional backup. Lose one key file with old-school backups and you're staring down a road of rebuilding instead of a restore. Conversely, an image-level backup consolidates that server's state into one nice and tidy bundle.

All this sounds fine and well until you start to dig a little deeper into the processes whereby image-level backups go about quiescing that server prior to a backup. You see, pretty much every hypervisor-based virtualization solution has the capability to quiesce the server prior to starting the backup. This "snapshotting" mechanism ensures that the restored file has file system integrity.

But there's always been a problem with transactional databases that ride atop that file system. Though any traditional backup tools could quiet the server, none to date could reach into that server to tell these databases they needed a time out as well.

The result of this omission is that although image-level restores usually get your server back on-line relatively quickly, your Exchange, SQL and other transactional databases have the chance to return to service in an inconsistent state. This means running the necessary database utilities -- like ESEUTIL for Exchange -- to bring the database back to health.

Until now. I recently discovered that VizionCore's vRanger Pro v3.2 includes support for directly communicating with a Windows virtual machine's Volume Shadow Copy Service (VSS). This communication allows the backup engine to instruct the database to pause at the correct point in the backup so that the database will not return from a restore in an inconsistent state.

The vRanger documentation includes an in-depth discussion of how this works with VSS. The process is complex and yet elegant in its implementation. Now, we administrators get to shout for joy knowing that with the right products our virtualized databases can maintain transactional integrity -- and therefore complete restorability -- while we do our nightly backups.