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 or 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 out of the cache pool, while their data is written to regular pools transparently. The following diagram illustrates the Ceph cache tiering:
A cache tier is constructed on top of 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 HDDs with the type replicated or erasure. The entire client I/O request goes to the cache tier and gets a faster response...