Why is my .mds filesize 0 bytes?

i downloaded file that contained two files, a .mdf and a .mds.

the .mdf was about 4gigs, but the .mds was only 0 bytes. is that normal?
also, since it would only let me load the .mds on alcohol 120%, it really isn’t helpful and would give me “File contains no data”.

anybody know what might be wrong?