The SSD Cache feature improves read-only performance. SSD cache is a set of solid-state disks (SSDs) that you logically group together in your storage array.
SSD cache is a secondary cache for use with the primary cache in the controller DRAM. In controller cache, the data is stored in DRAM after a host read. In SSD cache, the data is copied from user-specified base volumes, and stored on two internal RAID volumes (one per controller) that are automatically created on the SSDs when you create an SSD cache. These volumes are used for internal cache processing purposes. These volumes are not accessible or appear in the user interface. However, these two volumes do count against the total number of volumes allowed in the storage array.
Using high performance SSDs to cache the data from the base volumes improves the application I/O performance and response times, and delivers sustained performance improvement across different workloads, especially for high-IOP workloads. Simple volume I/O mechanisms are used to move data to and from the SSD cache. After data is cached and stored on the SSDs, subsequent reads of that data are performed on the SSD cache, there by eliminating the need to access the base volume.