Learning Ceph - Second Edition

Erasure coding

In this and other chapters we've discussed Ceph's replication strategy for data protection. Ceph also offers EC as an alternative. EC has its roots in data transmission, where it is not uncommon for portions of the signal to drop out or suffer erasure (hence the name). Unlike protocols (like TCP) that merely detect lost data and arrange for retransmission, erasure codes are designed to mix replication right in with payload data. Thus, missing sections can be regenerated computationally at the receiving end, unilaterally without having to contact the sender. The Voyager planetary probes, notably exploited a type of erasure code for their transmissions. At Neptune, the round trip time to send a signal back to Earth and receive ...