Building Disaster Tolerant Serviceguard Solutions Using Metrocluster with EMC SRDF
Metrocluster with SRDF/Asynchronous Data Replication
Chapter 5 331
Metrocluster with SRDF/Asynchronous Data
Replication
The following sections presents concepts, functionality and requirements
for configuring Metrocluster using SRDF/Asynchronous data replication.
SRDF/Asynchronous delivers asynchronous data replication solutions
featuring a consistent and restartable copy of the production data at the
remote side. Metrocluster with EMC SRDF supports
SRDF/Asynchronous to further enhance and protect critical business
information. The topics discussed in this section are as follows:
• Overview of SRDF/Asynchronous Concepts
• Requirements for using SRDF/Asynchronous in a Metrocluster
Environment
• Preparing the Cluster for SRDF/Asynchronous Data Replication
• Building a Device Group for SRDF/Asynchronous
• Limitations and Restrictions
Overview of SRDF/Asynchronous Concepts
SRDF/Asynchronous provides a long-distance replication solutions with
minimal impact on performance. This protection level is intended for
customers requiring minimal host application impact, but need to
maintain a restartable copy of data at R2 site. Data is transferred from
R1 site to the R2 site in predefined timed cycles called delta sets, which
eliminates the redundancy of same track changes being transferred over
the link. In the event of a disaster at the R1 site or if SRDF links are lost
during data transfer, a partial delta set of data is discarded. However, a
dependent write consistent point-in-time copy of data is retained on the
target side. Figure 5-12 depicts the SRDF/Asynchronous data sets.
• At the R1 site, the capture cycle is collecting all new writes and
tagging them as belonging to cycle N. There is also a transmit cycle
(N-1) which is not receiving any new data, but is transferring the
data it has collected when it was the active cycle to the remote side.
The capture cycle switches roles from capture to transmit during the
cycle switch process and a new capture cycle is created.