- 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
Write operations in cascaded SRDF
In cascaded configurations, R21 devices operate as:
- R2 devices to devices in the R1 array
- R1 devices to devices in the R2 array
I/O to R21 devices includes:
- Synchronous I/O between the production site (R1) and the closest (R21) remote site.
- Asynchronous or adaptive copy I/O between the synchronous remote site (R21) and the tertiary (R2) site.
- The storage administrator can Write Enable the R21 to a host so that the R21 behaves like an R2 device. This allows the R21 -> R2 connection to operate as R1 -> R2, while the R1 -> R21 connection is automatically suspended. The R21 begins tracking changes against the R1.
This diagram shows the synchronous I/O flow in a cascaded SRDF topology.
When a write command arrives in the cache at Site B:
- The SRDF emulation at Site B sends a positive status back across the SRDF links to Site A (synchronous operations)
- Creates a request for SRDF emulations at Site B to send data across the SRDF links to Site C.
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