Asynchronous Replication for Heterogeneous Environments

Whitepapers SmartWrite SAN over WAN

• Synchronous
  • Continuous
  • All writes
  • MV & RV in parallel
• Asynchronous
  • RDR-only
  • Continuous
  • All writes
    
• Background Copy
  • Periodic
  • Workload-based
  • Only delta changes

RAID Inc's Xanadu storage offers two types of replication options:

• Dynamic Data Replication (DDR)
• Remote Data Replication (RDR)

These may be combined to implement whatever recovery configuration is required.   DDR creates replica volumes (RV) from main volumes (MV) within the same storage array. RDR creates RVs from MVs in different arrays. RDR uses Fibre Channel to link the two arrays, at up to 4 Gbps. Replication over long distances requires a pair of FC to IP adapters.  Both DDR and RDR offer Synchronous mode and Asynchronous mode:

• In Synchronous mode, data is written to the RV in parallel with the MV as soon as the write command is issued. The host is notified of write completion only after the write is complete on both the MV and RV. As with all other storage systems, Synchronous replication is practical only over Fibre Channel distances due to performance implications. Synchronous DDR is often called mirroring.
• In Asynchronous mode, the host is notified of completion of the write request at the completion of writing to the MV. The data is then copied from the MV to RV.  Even if  the RV is located a great distance from the MV, this mode has no negative performance impact to the host. This type of operation is often called asynchronous replication. 

Both types of replication  offer an additional asynchronous mode called Background Copy. Only delta changes from the last background copy replication are transmitted rather than every write, reducing the bandwidth required to maintain the RV.

The host is notified of write completion as soon as the write to the MV is complete. Changes are accumulated and periodically sent to the RV based on the setting of the “background copy level.”  This “background copy level”  ranges from one to five, where one means the replication is always done as the lowest priority task, regardless of disk array workload, and five means the replication is always done with highest priority, regardless of workload. Values in between one and five dynamically adjust the replication priority based on array workload, increasing it when workload is low and decreasing it when workload is high, thereby maximizing replication throughput while minimizing the potential performance impact of doing so.

But ultizing the data replication features of Xanadu with the connectivity of Qlogic multi protocol router, customers have the best solution at an optimal price for the following applications:

• Disaster recovery for business continuation
• Data Migration for applications
• Replication for backups
• Sharing SAN devices to improve utilization

For additional information, please contact technical sales at sales@raidinc.com or call 800-330-7335.