Delay in NFS write operation using Data Domain and Netbackup

Symptom:
A 5 minutes delay may be expired when Netbackup 6.x or 7.x writes to a EMC Data Domain via  NFS share.

21/2012 11:59:14 - connecting
02/21/2012 11:59:14 - connected; connect time: 0:00:00
02/21/2012 11:59:15 - Info bptm (pid=28467) start
02/21/2012 11:59:15 - Info bptm (pid=28467) using 131072 data buffer size
02/21/2012 11:59:15 - Info bptm (pid=28467) using 128 data buffers
02/21/2012 11:59:15 - Info bptm (pid=28467) start backup
02/21/2012 12:05:16 - begin writing
02/21/2012 12:05:38 - Info bpbkar (pid=28466) bpbkar waited 4885 times for empty buffer, delayed 4917 times
02/21/2012 12:05:38 - Info bptm (pid=28467) waited for full buffer 1 times, delayed 28 times

Cause:
Incorrect NFS mount options. Netbackup debug logs (BPMT) do not give any indication of why this delay is present even with VERBOSE = 5.

Resolution:
EMC recommend the following qualifiers (Kernel 2.6 or newer):

mount -t nfs -o hard,intr,nfsvers=3,tcp,bg rstr01:/backup /dd/backup

or /etc/fstab options (all in one line):

duplo01:/data/col1/backup2 /backup2 nfs nolock,hard,intr,nfsvers=3,tcp,retry=10,rsize=32768,wsize=32768,bg 0 0

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