Our NetAPP SAN uses something called "Fibre Channel" disks.
What are Fibre Channel disks, and does this mean that I can't replace them with a NetApp SATA or SAS disk?
This question appears to be off-topic. The users who voted to close gave this specific reason:
It's a hard disk with a FC interface.
Nope, you probably can't just arbitrarily replace one of them with a disk with a different interface, and different IO characteristics, especially in a storage array. But ask your vendor to be certain, or consult their documentation!
And, spend 30 seconds on Google, too.