OK SQL2008R2 is better but unfortunately it too just went out of mainstream support. However the issue is probably related to the VM configurations. First off even though the backups may be going to a different logical drive than the data it is likely just a partition off the same physical array underneath, especially if these are virtualized drives and not pass thru. So any traffic on one will potentially impact the other since they are really the one and the same physically. But the memory is a real killer here. I don't know what else is using that VM but 9GB is not a lot for the OS, SQL Server and what ever else is on that VM. This would be especially true if it also hosts the app itself. Do you have a MAX Memory value set for the SQL Server instance? If not you should definitely set it so that you always leave memory for the OS and any other apps that may need it. Otherwise you will get sloshing between SQL Server and the OS / apps for available memory. Again I don't know what you have running on that VM other than Windows and SQL Server but I would set the MAX Memory to leave 2GB at least for the OS.
EXEC sys.sp_configure N'max server memory (MB)', 7168 ; RECONFIGURE WITH OVERRIDE ; http://sqlmag.com/sql-server-2008/m...08-2008-r2