Help me understand backup size

[pufferdude]

I just got veeam installed yesterday (evaluating, hoping to like it enough to buy!) and have successfully manually backed up two VMs. The first was a generic Win2003 box used for management and its 50gig of drive space ended up taking about 23gig on disk. Nice!

However, I then backed up my Exchange 2007 VM and enabled the VSS support for the backup, and things were quite different. The VM has 150GB worth of total drive space, and what ended up on disk was about 144GB, EVEN THOUGH the server is only using about 75GB of that space. Why the difference? Is there something about VSS backups that makes them bigger? I wouldn't have expected ANY backup to be bigger than the actual data in the virtual disk, but that's what I'm seeing.

Any advice, or is this just the way it works?

[Gostev]

Hello Jim, and welcome to Veeam Community!

This thread should answer your questions (see my first response)
surprising compression and dedup results

[pufferdude]

Thanks, that was it. There is an online backup app that also runs on this server that creates large temp files and deletes them, thus "corrupting" the empty space for image backup purposes. I think I will create a separate drive in the VM and tell the app to write its temp files there, so that the actual data drive stays "empty" in its unused portions.