Not necessarily, since Cisco is a hardware/networking company, I would imagine that a lot of that data is VHDL (or some other hardware descriptor language), sch

Not necessarily, since Cisco is a hardware/networking company, I would imagine that a lot of that data is VHDL (or some other hardware descriptor language), schematics, and even compiled binary images. They would also be storing the tools they use to build the products themselves in there (compiler, linker, assembler, etc). I would also wager that a lot of the 15TB of data is historical in nature, a lot of that for products that aren't being made or sold anymore but for which the source code, compiled images, etc is still stored there. Version control is not necessarily just for source code or text files, and what better place to store these extra version-specific artefacts than in the version control system.