The system does not serve data from a Flash Cache or Flash Cache 2 module when a node is shutdown. However, the WAFL external cache preserves the cache during a graceful shutdown and can serve "warm" data after giveback.
The WAFL external cache can preserve the cache in Flash Cache modules during a graceful shutdown. It preserves the cache through a process called "cache rewarming," which helps to maintain system performance after a graceful shutdown. For example, you might shut down a system to add hardware or upgrade software.
Cache rewarming is enabled by default if you have a Flash Cache or Flash Cache 2 module installed. Cache rewarming is available when both nodes in an HA pair are running Data ONTAP 8.1 or later.