Verifique os respectivos manpages. man mount.nfs
aponta para man 5 nfs
para detalhes, que diz:
soft / hard Determines the recovery behavior of the NFS client after
an NFS request times out. If neither option is
specified (or if the hard option is specified), NFS
requests are retried indefinitely. If the soft option
is specified, then the NFS client fails an NFS request
after retrans retransmissions have been sent, causing
the NFS client to return an error to the calling
application.
Portanto, o padrão, a menos que seja especificado de outra forma para o NFS, é difícil.
E man mount.cifs
diz:
soft
(default) The program accessing a file on the cifs mounted file
system will not hang when the server crashes and will return errors
to the user application.
E o padrão para o CIFS é suave.