Ceph's default replication level provides excellent protection against data loss by storing three copies of your data on different OSDs. However, storing three copies of data vastly increases both the purchase cost of the hardware and the associated operational costs, such as power and cooling. Furthermore, storing copies also means that for every client write, the backend storage must write three times the amount of data. In some scenarios, either of these drawbacks may mean that Ceph is not a viable option.

Erasure codes are designed to offer a solution. Much like how RAID 5 and 6 offer increased usable storage capacity over RAID 1, erasure coding allows Ceph to provide more usable storage from the same raw capacity. However, also like the parity-based RAID levels, erasure coding brings its own set of disadvantages.