Figure 48 SRDF/AR 3-site solution
SRDF/S
Site A Site C
Host
Site B
R1
R2
Host
TimeFinder
R1
TimeFinder
SRDF adaptive
copy
R2
If Site A (primary site) fails, the R2 device at Site B provides a restartable copy with
zero data loss. Site C provides an asynchronous restartable copy.
If both Site A and Site B fail, the device at Site C provides a restartable copy with
controlled data loss. The amount of data loss is a function of the replication cycle time
between Site B and Site C.
SRDF and TimeFinder control commands to R1 and R2 devices for all sites can be
issued from Site A. No controlling host is required at Site B.
Use SRDF/AR 3-site solutions to:
l
Reduce required network bandwidth using incremental resynchronization between
the secondary SRDF target site and the tertiary SRDF target site.
l
Reduce network cost and improve resynchronization time for long-distance SRDF
implementations.
l
Provide disaster recovery testing, point-in-time backups, decision support
operations, third-party software testing, and application upgrade testing or the
testing of new applications.
Requirements/restrictions
In a 3-site SRDF/AR multi-hop solution, SRDF/S host I/O to Site A is not
acknowledged until Site B has acknowledged it. This can cause a delay in host
response time.
TimeFinder and SRDF/A
In SRDF/A solutions, device-level pacing:
l
Prevents cache utilization bottlenecks when the SRDF/A R2 devices are also
TimeFinder source devices.
l
Allows R2 or R22 devices at the middle hop to be used as TimeFinder source
devices. Device-level (TimeFinder) pacing on page 134 provides more information.
Device-level write pacing is not required in configurations that include Enginuity 5876
and HYPERMAX OS.
Blended local and remote replication
162 Product Guide VMAX 100K, VMAX 200K, VMAX 400K with HYPERMAX OS
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