Creating a Mirrored Volume in a Remote Storage System with REC (Synchronous Mode)

This section describes the operations to create a mirrored volume of an operation volume (volume with the same data as the operation volume) on a remote storage system using the REC feature in synchronous mode. When a synchronous REC Session writes data to an operation volume, the data in the operation volume and the mirrored volume are always the same because the data write to the operation volume is completed after the data copy to the mirrored volume is completed. As a result, mirrored volumes can be used to guarantee data even if the storage system containing the business volume is damaged due to a disaster.

Caution

Since data is transferred to the remote storage system in synchronization with data writing to the operation volume, the response performance of the operation volume degrades according to the line performance of the copy path. Use in an environment where data transfer to the remote storage system can be performed with low delay. If you are transferring data over a long distance, if the line bandwidth of the copy path is small, or if you want to minimize the performance impact on operation volumes, consider using REC in asynchronous consistency mode or asynchronous stack mode.

RESTful API and Sample Scripts for Operation Use

  • Preparation

    Create a volume on the remote storage system that is the same size as the operation volume, and create an REC Session (synchronous mode) between the operation volume and the created volume. Use rec_sync_create.py.

  • Operation

    No action is required. After the initial copy is complete after the REC Session is created, the data in the operation volume and the mirrored volume are always consistent.

    If you want to temporarily switch the transfer mode to asynchronous consistency or asynchronous stack to prevent server response delays, use PATCH /copysession/{copysession_id} API.

  • Restore

    When restoring operation volume data from a mirrored volume, the REC Session is reversed and data is transferred from the remote to the local storage system, after recovery of the copy path and RAID Group if necessary. For REC Session inversion, rec_sync_consis_recover.py can be used.

  • Deletion

    If you want to remove a mirrored volume, force delete the REC Session, and then remove the destination volume. For forced deletion of the Copy Session, use DELETE /copysession/{copysession_id} API. For deletion of volumes, use DELETE /volume API. For more information, see the description of Deleting a Copy Session or Deleting Multiple Volumes.

    To remove only the REC Session and continue to use the mirrored volume in the remote storage system, remove only the REC Session. Use copysession_delete.py.

Notes

  • To avoid delays in update requests from the server, the REC Session status may transition to "Error" if forwarding to the destination is delayed because of the high load on the destination. In this case, remove the cause of the data transfer delay and delete and recreate the "Error" session. If you switch to "Error" again, consider using another transfer mode.

  • You can create up to eight mirrored volumes for a single business volume. The maximum number is smaller when using Snapshot or Clone backups together. For more information, see the description of multi-copy in "Available Advanced Copy Combinations" in "Design Guide".