Commvault® Stream Management

Data Streams are used to move data from source to destination. The source can be production data or Commvault protected data. A destination stream will always move to Commvault protected storage. Understanding the data stream concept will allow a CommCell^® environment to be optimally configured to meet protection and recovery windows.

Stream settings are configured in various places within the CommCell^® console including the storage policy, MediaAgent, subclient, and library. The system always uses the lowest setting. If a MediaAgent is configured to receive as many as 100 streams and one storage policy is writing through the MediaAgent and is configured to use 50 streams, then only 50 streams will be sent through the MediaAgent.

During a data protection job, streams originate at the source file or application that is being protected. One or more read operations are used to read the source data. The number of read operations is determined by the number of subclients and within each subclient, the number of data readers or data streams, depending on which agent is managing the data. Once the data is read from the source it is processed by the agent and then sent to the MediaAgent as job streams. The MediaAgent then processes the data, arranges the data into chunks and writes the data to storage as device streams. The data is written to storage based on the number of writers, for a disk library, or devices (tape drives) for a tape library.

Stream management high level overview

Stream Settings Summary Table

Features & Functionality	Description
Subclients	Subclients are independent jobs, each subclient will have one or more streams associated with each job.
	Most subclients can be multi-streamed. For subclients that do not support multiple streams, multiple subclients are used to multi-stream data protection jobs. Agents such as the new Exchange Mailbox agent manage streams at the object level. For Exchange, each mailbox is protected as a single stream. Data readers are configured in the General tab of the subclient. Data Streams are configured in the storage device tab for MS-SQL and Oracle subclients.
Non-Subclient based agents	Agents such as the new Exchange Mailbox agent manage streams at the object level. For Exchange, each mailbox is protected as a single stream. The default subclient data readers setting is still used as the primary stream governor for the maximum number of concurrent objects that can be protected.
Job Streams	Job streams are active network streams moving from source (client or MediaAgent) to destination (MediaAgent). The Job controller shows the total number of job streams currently in use in the bottom of the window and the job stream 'high watermark' for the CommCell^® environment. Add the 'Number of Readers in Use' field in the job controller to view the number of streams being used for each active job.
Device Streams	Configured in the Storage Policy properties. Determines how many concurrent write operations will be performed to a library. This number should be set to equal the number of drives or writers in the library to maximize throughput. Multiplexing is used to consolidate multiple job streams into single device streams.
Drives	For a removable media library writing data sequentially to devices, there will be one device stream per drive.
Writers	For a disk library where random read/write operations can be performed the number of writers should be set to allow the maximum throughput without creating bottlenecks in your network, MediaAgents, or disks.