<span>Like erasure-coding, the cache tiering feature has also been introduced in the Ceph Firefly release. A cache tier provides Ceph clients with better I/O performance for a subset of the data stored in a cache tier. A cache tiering creates a Ceph pool on top of faster disks, typically SSDs. This cache pool should be placed in front of a regular, replicated erasure pool such that all the client I/O operations are handled by the cache pool first; later, the data is flushed to existing data pools. The clients enjoy high-performance from the cache pool, while their data is written to regular pools transparently. The following diagram illustrates Ceph cache tiering:

A cache tier is constructed on top of an expensive, faster SSD/NVMe, thus it provides clients with better I/O performance. The cache tier is backed up by a storage tier, which is made up of...