When using invalidation mode w/storeAsBinary enabled, both the cache key and value are serialized during a cache put. However, unlike the cache key, the cache value will never be sent over the wire - so it seems that this serialization cost is necessary. Since INVALIDATION_SYNC is the default mode for hibernate 2nd level caching of entities and collections, and since serializing an entity is potentially costly, this performance hit very noticeable, especially when compared to the performance of JBoss Cache, where serialization only happens when needed.