NFS: freeze during copy

[rvenne at dental-on-line.fr]

Hi

I try to connect NFS client.

on the server:
/etc/rc.conf:
rpcbind_enable="YES"
nfs_server_enable="YES"
mountd_flags="-r"

10029  ??  Ss     0:00.02 rpcbind
10031  ??  Is     0:00.03 nfsd: master (nfsd)
10032  ??  I      0:00.00 nfsd: server (nfsd)
10033  ??  I      0:00.00 nfsd: server (nfsd)
10034  ??  I      0:00.00 nfsd: server (nfsd)
10035  ??  I      0:00.00 nfsd: server (nfsd)
10037  ??  Is     0:00.01 mountd -r

cat /etc/exports
/usr/data/backup -maproot=admin:wheel 192.168.254.2

client:
 83  ??  DL     0:00.03 [nfsiod 0]
   84  ??  DL     0:00.00 [nfsiod 1]
   85  ??  DL     0:00.00 [nfsiod 2]
   86  ??  DL     0:00.00 [nfsiod 3]

/etc/rc.conf: nfs_client_enable="YES"

I was able to mount nfs mounting point and to copie 16K of 7G data. and, 
it goes to freezing. I can't kill neither cp process neither mount 
unmount nfs (umount command goes freezing too). tcpdump tells me that 
server doesn't give any response in spite of client's udp queries.

need helps. thx