Dummy files can be very helpful in a Server environment. For example, having a 5 GB dummy file on the log and database partitions of an Exchange Server will help you resolve a space issue quickly. Simply delete the dummy file, and then you’d have some time to address the issue properly.
Use below Windows Commands to create dummy files in a size of your choice. 1 GB dummy file (1024*1024*1024=1073741824):
fsutil file createnew dummy.file 1073741824
5 GB dummy file (1024*1024*1024*5=5368709120):
fsutil file createnew dummy.file 5368709120