Ozone namespace concepts

The Ozone namespace includes the following conceptual entities: volumes, keys, and buckets. Each key is part of a bucket, which, in turn, belongs to a volume. Only an administrator can create volumes. Depending on their requirements, regular users can create buckets in volumes. Ozone stores data as keys inside these buckets.

The three main entities can be explained as follows:

Volume: An Ozone volume is similar to a user account, for example; sales, marketing, engineering, and so on.
Buckets: An Ozone bucket is similar to a directory or an Amazon S3 bucket. A bucket any number of keys but cannot contain other buckets.
Keys: An Ozone key is similar to any key in an object store or a file in a filesystem. If a key is used as a filesystem, the prefixes are treated as directories.

The following image depicts the relationship between volumes, buckets, and keys in the Ozone namespace:

When a client writes a key, Ozone stores the associated data on DataNodes in chunks called blocks. Therefore, each key is associated with one or more blocks. Within a DataNode, multiple unrelated blocks can reside in a storage container. Storage container is an internal Ozone abstraction that represents a collection of blocks and that singularly forms the unit of replication in Ozone.