Ceph is a distributed, failure-safe storage system that allows to redundantly store files etc. on the permanent storage (i.e. harddisks) of several computers ("nodes") at different locations which are connected e.g. via the internet. If one of the nodes fails (e.g. data center burns up), everything is still available on the remaining nodes.

POET memory++ on the other hand is no harddisk storage, but in the SRAM and DRAM configuration will be used as fast internal memory inside a computer.

However, with Flash, SSD storage, and POET memory++ in the NVRAM configuration as well as with fast memory caches in harddisk devices the boundaries become more and more blurred.

Anyway, Ceph is agnostic of whether a storage device is a traditional harddisk, an SSD, or a POET memory++ permanent storage.