There is actually a large number of request types in NFS. There are gettaddrs and other types of metadata requests that are used to read or change the access times, modified times, permissions, et al.
One example in my environment: We had a FAS960 running 36000 NFS ops a second. But inside that huge number was less than 500 reads/writes a second. The nature of the application using the NFS mounts required frequent scans of file attributes in a large file-count environment.
These "other" operations are often light, and don't add as much "real" workload to the filer as a pure large read or write would (as illustrated by the example).
