Are they? Right now? How do you know?

Run a quick benchmark locally and across the purported gigabit link both - SQLIO is my favorite quick tool for that, but a basic file copy will work, too. Do it both ways, just in case.

Note that when a disk controller loses its cache, or its battery (which almost always then disabled the cache), you can see a sudden dramatic drop in write performance.

If nothing else, get the HW folks to run online or offline diagnostics on both ends, the end that's being written to first.