Gaurav,
If you are planning to do it yourself, consider free tools like LVM mirroring or DD or RSYNC.
LVM Mirroring is ideal for any type of data and requires less down time (< an hour).
RSYNC is ideal if ‘file system’ data, and requires longer down time (few hours) depends on the rate of data change.
If planning to outsource, please consult with your NetApp sales or EM. Vicom offers appliance based fixed price simple and fast migration service (1.2 TB/Hour) with service guarantee (~$2K to 3K/server). This includes discovery, planning, preparation, appliance based migration and post-migration clean-up. No need to buy special hardware or software. Vicom is NetApp CDP. Migrated so far 5.5 PB of data and 250+ engagements.
Check out
http://www.vicom.com/solutions/solutions_vicom.htm
http://www.netapp.com/us/services/professional/san-data-migration.html
FYI, I am Vicom employee. Mail me if you need help in doing the migration yourself using free tools or regarding migration service.
-Vikas Aggarwal