Ozone architecture

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:
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. The SCM allocates blocks inside storage containers for the client to store data.
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 contain storage containers comprising of data blocks. The SCM monitors DataNodes through heartbeats.
Ozone Manager
The Ozone Manager (OM) is the metadata manager for Ozone. The OM manages the following storage elements:
  • The list of volumes for each user
  • The list of buckets for each volume
  • The list of keys for each bucket
The OM maintains the mappings between keys and their corresponding Block IDs. When a client application requests for keys to perform read and write operations, the OM interacts with the SCM for information about blocks relevant to the read and write operations, and provides this information to the client. In addition, the OM also handles metadata operations from the clients.
Hadoop Distributed Data Store
The Hadoop Distributed Data Store (HDDS) is a distributed block storage layer for Ozone.
Storage Container Manager
The Storage Container Manager performs multiple critical functions for an Ozone cluster.
The SCM manages the addition and removal of DataNodes, and allocates storage containers and blocks. The SCM also manages block collections, ensuring that the blocks maintain the required level of replication. The SCM allocates blocks to clients through the OM for read and write operations. In addition, the SCM executes recovery actions when faced with DataNode or disk failures.
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.