- Notes, cautions, and warnings
- Preface
- Introduction
- Disaster recovery
- High availability
- Data migration
- SRDF I/O operations
- SRDF write operations
- SRDF read operations
- SRDF/A resilience and performance features
- Management tools
- More information
Dell SRDF Introduction
Independent disaster recovery
Devices in SRDF/Metro groups can simultaneously be part of device groups that replicate data to a third, disaster-recovery site.
Either or both sides of the Metro region can be replicated. An organization can choose which ever configuration that suits its business needs. The following diagram shows the possible configurations:
The device names differ from a stand-alone SRDF/Metro configuration. This difference reflects the change in the devices' function when disaster recovery facilities are in place. For instance, when the R2 side is replicated to a disaster recovery site, its name changes to R21 because it is both the:
- R2 device in the SRDF/Metro configuration
- R1 device in the disaster-recovery configuration
When an SRDF/Metro uses a witness for resilience protection, the two sides periodically renegotiate the winning and losing sides. This means that the R1 side of the pair can change based on that witness determination of the winner. If the winning and losing sides do switch:
- An R11 device becomes an R21 device. That device was the R1 device for both the SRDF/Metro and disaster recovery configurations. Now the device is the R2 device of the SRDF/Metro configuration but it remains the R1 device of the disaster recovery configuration.
- An R21 device becomes an R11 device. That device was the R2 device in the SRDF/Metro configuration and the R1 device of the disaster recovery configuration. Now the device is the R1 device of both the SRDF/Metro and disaster recovery configurations.
Replication modes
As the diagram shows, the links to the disaster-recovery site use either SRDF/Asynchronous (SRDF/A) or Adaptive Copy Disk. In a double-sided configuration, each of the SRDF/Metro arrays can use either replication mode.
There are several criteria that a witness takes into account when selecting the winner side. For example, a witness might take DR configuration into account.
Operating environment
In a HYPERMAX OS environment, both SRDF/Metro arrays must run HYPERMAX OS 5977.945.890 or later. The disaster-recovery arrays can run Enginuity 5876 or HYPERMAX OS 5977.691.684, and later.
In a PowerMaxOS 5978 environment, both SRDF/Metro arrays must run PowerMaxOS 5978.144.144 or later. The disaster recovery arrays can run PowerMaxOS 5978.144.144, and later, HYPERMAX OS 5977.952.892, and later, or Enginuity 5876.288.195, and later.
SRDF/Metro configurations that can consist of a mix of operating environments. In this case, the SRDF and NDM Interfamily Connectivity Information defines the valid SRDF/Metro combinations and the operating environments that are valid for the disaster recovery arrays.
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