Backup - Somebody has to do it!

Not necessarily a glamorous topic I know, but absolutely essential as part of any deployment.

Contrary to popular belief (or what other vendors might have you believe) you don't need to re-engineer your backup infrastructure or license new technology if you're using virtualization. One of the benefits of virtualization with Windows as the host OS is that we have 20+ years of partners who have worked with us to ensure you get a well integrated backup and recovery solution. That's not to say that virtualization doesn't provide new opportunities for efficiencies, it most certainly does, but our philosophy is that you should be able to back up physical and virtual machines with a single tool (one you probably already have) while still taking advantage of the new benefits.

One of the things that virtualization makes easier is what is commonly called "bare metal recovery". This is the recovery situation you'd find yourself in if you wanted to completely rebuild a server after hardware failure or a disaster. With physical servers this can be tricky since the server that you backed up might not be identical to the server that you're restoring to. In addition, unless you're using an imaging tool, recovery typically involves laying down a fresh copy of the OS before you can even begin to get your application and data back which can kill your SLA. With VMs, you have the opportunity to back up the entire virtual machine (at the VHD level) so that bare metal recovery simply involves copying your VHDs to any host server. There's a not so subtle catch here though - how do you ensure that your VHDs are in a "consistent" state so that recovery will actually work? You could shut down the VMs before backup or save state but that's not particularly appealing for obvious reasons. You could just grab the VHDs while the VM is running and hope that the recovery works....which is equally unappealing. What you really need is a way to back up the VMs at the host (VHD) level but ensure that that the data within the VHDs is consistent and recoverable without downtime.

The Windows platform provides just such a mechanism and it's called the Volume Shadow Copy Service or VSS. VSS allows for application-coordinated backups using snapshot technology. Every one of our server applications and subsystems (SQL, Exchange, Sharepoint, registry, DNS etc.) comes with a VSS plug-in known as a "VSS Writer". When a backup system asks for a snapshot of a server, the VSS infrastructure goes through all of the VSS writers on a system and asked them to get their on-disk data into a consistent state (flush buffers, finish or rollback mid-flight transactions etc.) so that backup applications can grab the files. There's a much more orchestration than that involved but for the purposes of this discussion, the simplification I've made is sufficient. We actually use the same infrastructure on our desktop OS versions starting with XP....if you're really bored, open a command prompt and type "vssadmin list writers" and you'll get back a list of VSS writers installed on that system. The reason we have application vendors build the writers is because only the application knows how to get itself into a consistent state and every application is different.

Starting with Virtual Server R2 SP1 and also available in Hyper-V, we've included a VSS writer for virtual machine backup. This has allowed products like System Center Data Protection Manager (DPM) and products from our partners to install a single agent on the virtual machine host and ensure that you get consistent, recoverable copies of your VMs. Using the VSS framework and the application-specific writers, when the backup agent initiates a backup request, the host OS automatically communicates with all of the applications running inside of the VMs to ensure that they get themselves into a consistent state so that the data contained within the VHD is application consistent. That way, the recovery is not only guaranteed to work but you won't have to sit through a 2 hour chkdsk or consistency check session.

DPM has a pretty slick UI to make backup and recovery easy and includes the ability to backup to disk and tape in an integrated way. If you've got SCVMM, you're already licensed for DPM so give it a try. If you're not using DPM, check with your backup vendor to see if they include support for virtual machine backup on Virtual Server and Hyper-V, most of them already do.

Bottom line - if you're virtualizing on Windows, backup and recovery will snap into place seamlessly with your existing infrastructure.

Rakesh

Comments

• Anonymous
  January 01, 2003
  Hi Rakesh, Microsoft recommends running ESEUtil on a VSS Exchange storegroup backup. Unlike a streamed backups, checksum is not verified in VSS backups. Do I need to run chkdsk on a VSS hyper-v backup to ensure the backup is prestine and good?