NFS performance very slow with 'tar' command but much faster with 'dd'

Issue

Creating a tar and extracting , I am getting very low speed like 6-10MB/sec. It is writing to netapp filer and NFS mounted
- To create tar file of 444GB it took 12 hours
- To extract 444GB tar file it took 18 Hours
DD's will give me 80MB/sec speed.
- CPU is not 100% used

Red Hat Enterprise Linux 5.4
- 2.6.18-164.6.1.el5
- nfs-utils-1.0.9-42.el5-x86_64
Application: 'tar' command
- source: GFS filesystem (EMC) or NFS server (NetApp)
- destination: NetApp NFS Server
NetApp FAS3240 (NFS Server)
- Ontap version: 8.0.1P5 7-mode

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