This is an issue that VDI deployments always run in to.
The symptom is this: I deployed bunches of VDI VMs. Folks begin using them. And a week goes by. Suddenly I notice that most all the reserve storage that I had planned on is gone.
I don’t have any snapshots happening. I check that the backup software isn’t leaving weird VSS backups or temporary files lying around. I even look for AVHDs (though I know there should not be any).
So what happened?
I go looking around and I see all these .BIN and .VSV files.
The VSV is a small placeholder.
However, the BIN is equal in size to the amount of RAM that the running VM is consuming. If you have Dynamic Memory enabled, it equals the amount of Assigned Memory – so it changes.
Therefore, Dynamic Memory on, means that you design for the worst case scenario – calculate for the Maximum Memory setting of all the VMs stored on that particular LUN.
What this will cause you to do is:
- Realize the impact that this BIN file has on storage.
- Be smart about setting the Maximum Memory of your VMs.
- Understand the risk and accept the risk and push forward without making any considerations.
If you have read this far you might be thinking, What is this BIN file for anyway?
It is a safety net for your VM(s).
It is a placeholder that reserves storage on the file system, so that if the hypervisor needs to reboot, it can quickly dump the memory of your VM(s) to disk.
This does not help you if the hypervisor crashes due to something like a bad driver, this is Hyper-V being able to respond to something and save your VMs – Oh, such as when you run out of storage and it puts your VMs into a saved state. That is one use.