Ozone architecture

Ozone can be co-located with HDFS with single security and governance policies for easy data exchange or migration and also offers seamless application portability. Ozone has a scale-out architecture with minimal operational overheads. Ozone separates management of namespaces and storage, helping it to scale effectively. The Ozone Manager (OM) manages the namespaces while the Storage Container Manager (SCM) handles the containers.

The following diagram shows the components that form the basic architecture of Ozone:
Hadoop Distributed Data Store
Ozone is built on a highly available, replicated block storage layer called Hadoop Distributed Data Store (HDDS).
Ozone Manager
The Ozone Manager (OM) is a highly available namespace manager for Ozone.

OM manages the metadata for volumes, buckets, and keys. OM maintains the mappings between keys and their corresponding Block IDs. When a client application requests for keys to perform read and write operations, OM interacts with SCM for information about blocks relevant to the read and write operations, and provides this information to the client. In addition, OM also handles metadata operations from the clients.

Blocks
Blocks are the basic unit of storage. In Ozone, each block is of 256 MB in size. A collection of blocks forms a storage container.
Storage Containers
A storage container is a group of unrelated blocks managed together as a single entity. A container exists in a DataNode and is the basic unit of replication, with a capacity of 2 GB to 16 GB.
DataNodes
DataNodes contain storage containers comprising of data blocks. The DataNodes are monitored by the Storage Container Manager (SCM) through heartbeats.
Storage Container Manager
The Storage Container Manager performs multiple critical functions for an Ozone cluster.
SCM manages the addition and removal of DataNodes, and allocates storage containers and blocks. SCM also manages block collections, ensuring that the blocks maintain the required level of replication. SCM allocates blocks to clients through OM for read and write operations. In addition, SCM executes recovery actions when faced with DataNode or disk failures.
Pipelines
Pipelines determine the replication strategy for the blocks associated with a write operation.
Recon Server
Recon is the management interface for Ozone. Recon provides a unified management API for Ozone.