Streams - Advanced

Table of Contents

The following sections describe how you can manage device streams that are used for copy operations (such as auxiliary copy or data verification operations, or data protection operations that create inline copies).

Configuring the File System Multi-Streaming

File System Multi-Streaming uses multiple data streams per subclient for the backup jobs. Multi-Streaming enables the subclient's contents to be distributed to all the streams, transmitting them in parallel to the storage media. Hence a subclient whose data is secure using three data streams, uses more of the available network resources, and can complete in as little as one third the time that the same data would require using a single stream.

File System Multi-Streaming allows you to take advantage of the fast read access from the array and improve the rate at which the data can be written to the storage media.

Notes:

  • Do not enable multi-streaming if you have multiple mount points pointing to the same physical drive.
  • For Windows Agents, the read throughputs for multiple data readers on the same physical disk might degrade the write performance.
  • For Unix Agents, the read throughputs for multiple data readers on different mount points on the same disk may vary depending on the hardware.

To configure the File System Multi-Streaming:

  1. From the CommCell Browser, expand Client Computers > client > backupset.
  2. Right-click the appropriate subclient or instance, and then click Properties.
  3. In the Subclient Properties or Modify Instance Properties dialog box, select the Allow multiple data readers within a drive or mount point check box.

    When multi-streaming is set, multiple simultaneous data readers are allowed on each drive (or mount path, for Unix) during the backup operation.

Setting Number of Streams for an Auxiliary Copy

By default, all the data streams on the primary copy are simultaneously copied to a secondary copy. The data gets copied stream by stream. If there are four data streams on the primary copy, then the auxiliary copy operation uses four device streams on the secondary copy.

If sufficient storage resources are not available, or you do not want to use all of the available resources, you can select the number of device streams that are copied simultaneously during an Auxiliary Copy operation.

To specify the number of device streams:

  1. From the CommCell Browser, expand Policies > Storage Policies.
  2. Right-click the storage_policy, click All Tasks > Run Auxiliary Copy.
  3. Select Number of Streams and then specify the number of device streams.

    If enough storage resources are available, you can select Allow Maximum so that all of the data streams are copied simultaneously during an Auxiliary Copy operation.

  4. Click OK.

Enabling Combine Stream

When the secondary copy has fewer device streams than the primary copy, you can use the combine streams from the primary copy while the copy operation is performed. If you enable this option, the secondary copy of the data uses less media than the media required for the backup data. This improves media usage because the media storage is optimized. Media recycling is also more efficient, because data aging is more effective.

To enable the combine streams option for a secondary copy:

  1. From the CommCell Browser, expand Policies > Storage Policies > storage_policy.
  2. Right-click the appropriate storage policy copy, and then click Properties.
  3. In the Copy Properties dialog box, click the Media tab, select the Combine source data streams to check box, and then specify the number of streams.

    Notes:

    • The DB2, DB2 MultiNode and Sybase agents use same number of streams for restore operation that are used during backup even if Combined Streams option is configured on the storage policy copy.
    • If you are performing a restore operation from a secondary copy that has the Combined Source Data Stream to option enabled:
  4. Click OK.

Combining Streams Using Data Multiplexing

When you select the Combine source data streams option for a secondary copy, you can also enable multiplexing for the secondary copy. When you enable data multiplexing, multiple data streams are copied simultaneously to the same media. This optimizes performance of the copy operation in a disk environment.

  1. From the CommCell Browser, expand Policies > Storage Policies > storage_policy.
  2. Right-click the appropriate storage policy copy, and then click Properties.
  3. In the Copy Properties dialog box, click the Media tab, and the specify the appropriate settings.
    1. Select Combine source data streams to check box and then specify the number of streams.
    2. Select Multiplexing source streams check box and then enter the Multiplexing Factor.

      Enable this option when the storage policy copy is configured with combine streams and the copy does not contain deduplicated data.

  4. Click OK.

Configuring Stream Randomization

When a storage policy is configured to use more than one device stream, it is important that the device streams are equally used. If you enable stream randomization, the system chooses the device streams randomly. This increases the rate of data transfer by copying data from different streams in parallel.

To enable stream randomization:

  1. From the CommCell Browser, expand Policies > Storage Policies.
  2. Right-click the appropriate storage policy copy, and then click Properties.
  3. Select the Enable Stream Randomization check box.
  4. Click OK.

You configure the tuning parameters to evenly distribute the data across all of the streams. You can specify the interval to check the data size in the streams and the threshold to decide data distribution among the streams. Refer to Tunable Parameters for more information on tuning stream randomization.

Configuring Dynamic Stream Allocation

When data is not distributed equally across all of streams on the source copy, then one stream might take longer to copy than another. You can avoid this situation by distributing data across multiple streams.

Auxiliary Copy operation is performed with a fixed mapping between the source and destination streams. If the original backup data was not distributed evenly in the source streams, the Auxiliary Copy operation may not use all of the available streams simultaneously. In such a situation, enabling Stream Randomization helps to distribute data evenly among streams. However, if a sufficient number of drives are not available for each stream during an Auxiliary Copy operation, the stream randomization might not be ineffective. Dynamic Stream Allocation feature allow you to distribute data evenly across available streams and is most effective when the source copy is on a disk. This feature cannot be used when source copy is on tape because it cannot read randomly from tape media.

Dynamic Stream Allocation feature can also be used for the following operations to distribute the data between streams:

  • Content Indexing
  • Data Verification
  • Deduplication Database (DDB) Reconstruction

    When this feature is enabled, for these operations, the stream settings that are specified on the Copy Properties - Media tab have no effect, and dynamic stream allocation uses maximum number of device streams that are set in the Storage Policy properties.

You can enable this feature in the following scenarios:

  • When the Combine Source Data Streams and Multiplex source streams options are enabled for the a secondary copy.
  • When multiple Storage Policies are using same library and Auxiliary Copy jobs for all the storage policies are scheduled at the same time.
  • When some drives from the tape library are offline for long time.

To enable distribute data evenly across multiple streams for Auxiliary Copy:

  1. From the CommCell Browser, expand Policies > Storage Policies.
  2. Right-click the appropriate storage policy, and then click Properties.
  3. Select the Distribute data evenly among multiple streams for offline read operations check box, to distribute backup data evenly across multiple streams.
  4. Click OK.

    Note: When this option is enabled during Auxiliary Copy operation, the values of Total data to Process in the General tab of Auxiliary Copy Job Details dialog box and the sum of Total Data to View Jobs in the Jobs for Storage Policy Copy window will differ.