I've performed an upgrade and afterwards my cache age is higher. Before the upgrade it was ~3 minutes, now it is ~4.5 minutes. The amount of operations over NFS did not change. NFS latency also for all volumes is now 50% of the latency before the upgrade. 

Cache age with snmp from http://ipmsupport.solarwinds.com/mibs/NETWORK-APPLIANCE-MIB/item.aspx?id=miscCacheAge . It is "Age in minutes of the oldest read-only blocks in the buffer cache.  This indicates how fast read operations are cycling through system memory; when the appliance is reading very large files (larger than the machine's memory size), buffer cache age will be very low."

In the background there is still a rlw_upgrading process running, details in https://communities.netapp.com/thread/22676 .

So overall I think that lower nfs latency is better, but am not certain about cache age. Is it not strange both changed so much after the upgrade? Have you had similar experiences?

Best regards,

Rafal Radecki.