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| <h1>Ozone Manager</h1> |
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| <!--- |
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| limitations under the License. |
| --> |
| <p><img src="OzoneManager.png" alt="Ozone Manager"></p> |
| <p>Ozone Manager (OM) is the namespace manager for Ozone.</p> |
| <p>This means that when you want to write some data, you ask Ozone |
| Manager for a block and Ozone Manager gives you a block and remembers that |
| information. When you want to read that file back, you need to find the |
| address of the block and Ozone Manager returns it you.</p> |
| <p>Ozone Manager also allows users to organize keys under a volume and bucket. |
| Volumes and buckets are part of the namespace and managed by Ozone Manager.</p> |
| <p>Each ozone volume is the root of an independent namespace under OM. |
| This is very different from HDFS which provides a single rooted file system.</p> |
| <p>Ozone’s namespace is a collection of volumes or is a forest instead of a |
| single rooted tree as in HDFS. This property makes it easy to deploy multiple |
| OMs for scaling.</p> |
| <h2 id="ozone-manager-metadata">Ozone Manager Metadata</h2> |
| <p>OM maintains a list of volumes, buckets, and keys. |
| For each user, it maintains a list of volumes. |
| For each volume, the list of buckets and for each bucket the list of keys.</p> |
| <p>Ozone Manager will use Apache Ratis(A Raft protocol implementation) to |
| replicate Ozone Manager state. This will ensure High Availability for Ozone.</p> |
| <h2 id="ozone-manager-and-storage-container-manager">Ozone Manager and Storage Container Manager</h2> |
| <p>The relationship between Ozone Manager and Storage Container Manager is best |
| understood if we trace what happens during a key write and key read.</p> |
| <h3 id="key-write">Key Write</h3> |
| <p><img src="OzoneManager-WritePath.png" alt="Write Path"></p> |
| <ul> |
| <li> |
| <p>To write a key to Ozone, a client tells Ozone manager that it would like to |
| write a key into a bucket that lives inside a specific volume. Once Ozone |
| Manager determines that you are allowed to write a key to the specified bucket, |
| OM needs to allocate a block for the client to write data.</p> |
| </li> |
| <li> |
| <p>To allocate a block, Ozone Manager sends a request to Storage Container |
| Manager (SCM); SCM is the manager of data nodes. SCM picks three data nodes |
| into which client can write data. SCM allocates the block and returns the |
| block ID to Ozone Manager.</p> |
| </li> |
| <li> |
| <p>Ozone manager records this block information in its metadata and returns the |
| block and a block token (a security permission to write data to the block) |
| to the client.</p> |
| </li> |
| <li> |
| <p>The client uses the block token to prove that it is allowed to write data to |
| the block and writes data to the data node.</p> |
| </li> |
| <li> |
| <p>Once the write is complete on the data node, the client will update the block |
| information on Ozone manager.</p> |
| </li> |
| </ul> |
| <h3 id="key-reads">Key Reads</h3> |
| <p><img src="OzoneManager-ReadPath.png" alt="Read Path"></p> |
| <ul> |
| <li>Key reads are simpler, the client requests the block list from the Ozone |
| Manager</li> |
| <li>Ozone manager will return the block list and block tokens which |
| allows the client to read the data from data nodes.</li> |
| <li>Client connects to the data node and presents the block token and reads |
| the data from the data node.</li> |
| </ul> |
| <h2 id="main-components-of-the-ozone-manager">Main components of the Ozone Manager</h2> |
| <p>For a detailed view of Ozone Manager this section gives a quick overview about the provided network services and the stored persisted data.</p> |
| <h3 id="network-services-provided-by-ozone-manager">Network services provided by Ozone Manager:</h3> |
| <p>Ozone provides a network service for the client and for administration commands. The main service calls</p> |
| <ul> |
| <li>Key, Bucket, Volume / CRUD</li> |
| <li>Multipart upload (Initiate, Complete…) |
| <ul> |
| <li>Supports upload of huge files in multiple steps</li> |
| </ul> |
| </li> |
| <li>FS related calls (optimized for hierarchical queries instead of a flat ObjectStore namespace) |
| <ul> |
| <li>GetFileStatus, CreateDirectory, CreateFile, LookupFile</li> |
| </ul> |
| </li> |
| <li>ACL related |
| <ul> |
| <li>Managing ACLs if <a href="../security/securityacls.html">internal ACLs</a> are used instead of <a href="../security/securitywithranger.html">Ranger</a></li> |
| </ul> |
| </li> |
| <li>Delegation token (Get / Renew / Cancel)</li> |
| <li>For security</li> |
| <li>Admin APIs |
| <ul> |
| <li>Get S3 secret</li> |
| <li>ServiceList (used for service discovery)</li> |
| <li>DBUpdates (used by <a href="../feature/recon.html">Recon</a> downloads snapshots)</li> |
| </ul> |
| </li> |
| </ul> |
| <h3 id="persisted-state">Persisted state</h3> |
| <p>The following data is persisted in Ozone Manager side in a specific RocksDB directory:</p> |
| <ul> |
| <li>Volume / Bucket / Key tables |
| <ul> |
| <li>This is the main responsibility of OM</li> |
| <li>Key metadata contains the block id (which includes container id) to find the data</li> |
| </ul> |
| </li> |
| <li>OpenKey table |
| <ul> |
| <li>for keys which are created, but not yet committed</li> |
| </ul> |
| </li> |
| <li>Delegation token table |
| <ul> |
| <li>for security</li> |
| </ul> |
| </li> |
| <li>PrefixInfo table |
| <ul> |
| <li>specific index table to store directory level ACL and to provide better performance for hierarchical queries</li> |
| </ul> |
| </li> |
| <li>S3 secret table |
| <ul> |
| <li>For S3 secret management</li> |
| </ul> |
| </li> |
| <li>Multipart info table |
| <ul> |
| <li>Inflight uploads should be tracked</li> |
| </ul> |
| </li> |
| <li>Deleted table</li> |
| <li>To track the blocks which should be deleted from the datanodes</li> |
| </ul> |
| <h2 id="notable-configurations">Notable configurations</h2> |
| <table> |
| <thead> |
| <tr> |
| <th>key</th> |
| <th>default</th> |
| <th>description</th> |
| </tr> |
| </thead> |
| <tbody> |
| <tr> |
| <td>ozone.om.address</td> |
| <td>0.0.0.0:9862</td> |
| <td>RPC address of the OM. Required by the client.</td> |
| </tr> |
| <tr> |
| <td>ozone.om.http-address</td> |
| <td>0.0.0.0:9874</td> |
| <td>Default port of the HTTP server.</td> |
| </tr> |
| <tr> |
| <td>ozone.metadata.dirs</td> |
| <td>none</td> |
| <td>Directory to store persisted data (RocksDB).</td> |
| </tr> |
| </tbody> |
| </table> |
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