Multiple stream replication

Replication and Disaster Recovery Administration Guide for Hitachi NAS Platform

Part Number

Multiple replication streams are created by adding TCP connections between the source and target systems of a replication or ADC copy operation. Each additional connection is used for an additional data stream by the replication application.

Multi-stream replication helps to alleviate some latency problems found with single-stream replication by running multiple independent streams in parallel. When latency from sequentially executed functions limits performance, multiple independent streams can produce a significant performance improvement.

Multi-stream replication is only supported if both the source and destination systems are using software release 6.1 or later.

For policy-based replication operations, multi-stream replication is controlled using the replication Add Rule or Modify Rule pages of the NAS Manager.

For ADC copies, multi-stream support is enabled by setting the number of additional connections requested as the value of the environment variable NDMP_BLUEARC_MULTI_CONNECTION (refer to the Backup Administration Guide for more information).

Note the following:

  • When using software release 6.1 or later, and using multi-stream replication or embedded inline hard linked files, if a replication fails part way through, it will not be possible to restart replication if the server is downgraded to an earlier release. Refer to the Backup Administration Guide for more information about NDMP support for embedded hard links.
  • Multi-stream replication features are not enabled using the ndmp-option CLI command; instead, the invoking NDMP command must request multiple streams.

    For policy based replications the multi-stream feature is configured using replication rules.

    For individual ADC copies, multiple streams are specified by adding the NDMP_BLUEARC_MULTI_CONNECTION environment variable to the ADC script (refer to the Backup Administration Guide for more information).

  • NDMP has two ways of copying data from files with hard links. The NDMP_BLUEARC_EMBEDDED_HARDLINKS environment variable controls this behavior (refer to the Backup Administration Guide) for more information on this variable.
Note: When multiple connections/streams are used, the data from files with hard links is embedded within the hierarchical path data, regardless of the setting of the NDMP_BLUEARC_EMBEDDED_HARDLINKS variable.