Erasure Coding overview
The Ozone Erasure Coding (EC) feature provides data durability and fault-tolerance along with reduced storage space and ensures data durability similar to Ratis THREE replication approach.
The Ozone default replication scheme Ratis THREE has 200% overhead storage space including other resources. Using EC in place of replication helps in reducing storage cost as the overhead storage space is only 50%. For example, if you replicate 6 blocks of data, you need 18 blocks of disk space in Ratis. However, if you use EC with Ozone, you need 6 blocks plus 3 parity totalling to 9 blocks of disk space.
Write and read using EC
When a client requests write, OM allocates a block group (data and parity) number of nodes from the pipeline to the client. Client writes d number of chunks to d number of nodes. Parity chunks(p) are created and transferred to the remaining p number of nodes. After this process is completed, the client can request for a new block group after the writing of the current block group is finished.