Hello,
The user who commented on prices increasing for older filers is correct. If you perform a quick TCO on your filers, you might find it's cheaper to replace your F7XX filers with F8XX filers since the new filer can be purchased with a 3-year maintenance contract.
Depending on your pricing structure with NetApp, you might find you'll do better (save your company money) by refreshing your hardware every 2-3 years instead of drawing it out to 3-5 years.
/Brian/