WHen NFS was first implement, TCP was much slower than UDP.
This is not, however, true in general. TCP is much more complex to
implement correctly, but on a well-tuned implementation the overhead
is not significantly greater (on a modern processor, using a 10-Mbps
LAN).
There is one way in which UDP's overhead is lower than TCP's:
data checksums are optional in UDP (in IPv4). But:
1) NFS over UDP without checksums is a <b>bad idea</b>. People
have lost filesystems because of it.
2) On many (most?) modern computers, the checksum calculation can be
combined with a buffer copy at no additional cost.
Craig Milo Rogers