> Why is nfsd started 8 times? Does that improve nfs performance ?

The short answer is yes.  Basically, it means that there are up to eight
connections available, assuming that none are already being used by
other hosts.  Having threads available basically just means that there
will be less delay in waiting after a connection requst is made.

It depends on how many other hosts are accessing files on the host where
the nfs daemon is running.  As it's been at least 18 months since I've
worked with it, my memory is a little hazy, but I'll give it a shot.
There are two types of nfs support in Linux, at least with the 2.4
version kernels: kernel or user space - my experience was use of the
kernel "daemon", which I think offers performance advantage.  This
requires that your kernel is configured to provide nfsd support.

As I remember, the daemon initially starts with the number specified in
the config file.  The name and location of that file will depend on the
particular version of the distro that you're running.  If you're on a
LAN with say, less than 5 stations, 8 threads / instances of nfsd may be
superfluous.  But that also depends on how nfs is being used.  If you're
doing something like running a terminal server for thin clients, then
each client will require multiple nfs connections (one connection per
thread).  OTOH, if all you're doing is providing file access e.g.,
similar to a samba share, then it's more likely that there will be only
one thread used per client, and the delay to start another thread / nfsd
instance would likely be negligible.