If you have a lot of users using RDS with UPD enabled, there will be a lot of individual UDP files stored on the file share, named with the unique GUID of the AD user, like below:

So, how to identify which UPD disk belongs to which user account?

You can use the following PowerShell cmdlet to find out the user based on the GUID.

Get-ADUser -fileter {SID - like "GUID"}

Or, find out the GUID based on the user account ID.

Get-ADUser -filter {SamAccountName -like "UserID"}

Or, even better, use this little portable standalone tool called Sidder to help you to quickly identify which UDP belongs to which AD user. You will need .Net 4.5 Framework to use this tool.

The ones in orange are the ones that are in use at the moment. The tool also allows you to delete UPD as well. Deleting UPD will result in a fresh start for that user next time when they log in.