There's currently a discussion on the linux-kernel mailing list about testing very large filesystems (and LVM and md volumes). Since most people don't have a 15 TiB SAN available, they need a better way of doing this.
One approach would be to adapt the "COW disk images" that are used by some emulators, and produce a block device that pretends to be arbitrarily large but only stores changed blocks onto another device. This way, you could construct a very large filesystem for testing using a modest amount of disk space (provided you didn't want to store very much on it).