WAFL is used exclusively on network file servers produced by Network Appliance and is meant for use as a distributed file system.
It can provide files to clients via the NFS, CIFS, ftp,and http protocols, although it was designed just for NFS and CIFS.
When many clients use these protocols to talk to a file server, the server may see a very large demand for random reads and an even larger demand for random writes.
The NFS and CIFS protocols cache data from read operations, so writes are of the greatest concern to file-server creators.