SharePoint performance on slower drives

I'm looking into the option of archiving some existing SP data to a dedicated SP Records Management site. The RM would be configured to use its own DB. The DB would be located on a slower drive. The remaining drives including installation will remain on current fast drives.

The supplier has told be that this will affect SP overall performance as SP will assume the lowest drive speed. I cant see why this would happen, can this be true?

Thanks