Cache Acceleration enables you to create an SSD cache for improving the read performance of the NAS.
QES only uses the SSD cache for read-cache.
On ES series NAS models, QES perform write caching using hardware NVRAM.
TES and TDS series NAS models offer RAM write cache protection (write log) when you add an SSD to the SSD cache. The write log ensures data integrity and also helps increase write performance, but it is not technically a write cache.
Shared folders and LUNs created in an all-SSD storage pool cannot use the SSD cache, as it would provide no additional performance benefits.