I've had quite a few discussions lately about the rationale behind backing up VDI and whether it is necessary....
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At the end of the day, it depends on your existing PCs and the level of user customization.
The prevailing opinion boils down to whether you have a need to back up your physical desktops. If you do, then you might need to back up virtual desktops, too. But, if you're like most companies that do not back up their physical PCs, then virtual desktop infrastructure (VDI) backup is more or less unnecessary. That said, I think the topic is worth some exploration.
What drives the need to back up physical desktops?
Most people share the philosophy that a properly designed desktop does not need to be backed up. "Properly designed" means that the only things residing on the desktop are Windows and the applications.
If you already have a well-managed desktop, you probably don't need to back it up.
The profile and user data are stored elsewhere, presumably on a file server that is backed up. This could mean you have roaming profiles or a profile management tool that creates a compartmentalized user environment that's manageable separately from Windows. Applications are either part of the image or deployed through some automated method, which means that even a bare-metal rebuild of a system allows the user to access all their data, applications and user environment.
Does that mean that desktop backup is only for poorly-designed desktop environments? Not necessarily. If you back up physical PCs, it means you have found a specific business requirement that makes backups necessary. It could be that you have a handful of desktops that are far too customized not to be backed up.
Complex or custom software, settings, drivers, configurations and so on can also lead IT to back up a PC -- almost as if it were a server. This is a niche reason, but it's one that most of us can relate to (and one that also applies to virtual desktop backup).
What about virtual desktops?
Now that we've established a very limited use case for physical desktop backup, let's look at it from the perspective of VDI.
Conventional opinion is that you would back up your virtual desktops the same way you do physical desktops, so it might seem like the discussion should end right there. However, part of the advantage of VDI is that you're working with disk images rather than monolithic instances of Windows on a single disk. That means you have a bit more flexibility in terms of what you can back up and why.
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One example use case came from a friend on Twitter, who mentioned that he uses virtual disk snapshots as a rollback solution in 1:1 or persistent-image VDI environments. This method enables organizations to fall back to previous versions of a virtual machine (VM) in the event of a failure -- sort of like a low-level System Restore point. The snapshots themselves may be large, but block-level deduplication can optimize the storage so they take up a minimal amount of space. The Twitter user keeps four weeks' worth of weekly snapshots for rollback purposes. If that doesn't work, only then do they rebuild a user's VM.
Still, most experts don't feel the need to back up VDI, especially in a non-persistent or shared VDI environment. In that situation, the master Windows image is simply a virtual disk that is presumably backed up by conventional means. Plus, the users' personalities, data and applications are already compartmentalized and added on to the base image at run time. They should be backed up in those locations, but there is no need to back up the entire Windows image.
Persistent VDI doesn't appear to open up many new needs for desktop backup beyond the occasional snapshot. I'm curious to learn about other potential uses for VDI backup, though, so I encourage you to share your thoughts in the comments. I do like the rollback feature, but I'm not sold on it all by itself. Time will tell, but until then keep following common sense. If you already have a well-managed desktop, you probably don't need to back it up.