secondary site until no new writes are sent to the R1 device and all data has
finished copying to the R2.
SRDF 2-site solutions
The following table describes SRDF 2-site solutions.
Table 39 SRDF 2-site solutions
Solution highlights Site topology
SRDF/Synchronous (SRDF/S)
Maintains a real-time copy of production data at a
physically separated array.
l
No data exposure
l
Ensured consistency protection with SRDF/
Consistency Group
l
Up to 125 miles (200 km) between arrays
See: Write operations in synchronous mode on page
127.
Primary Secondary
Limited distance
R1
R2
Synchronous
SRDF/Asynchronous (SRDF/A)
Maintains a dependent-write consistent copy of the
data on a remote secondary site. The copy of the
data at the secondary site is seconds behind the
primary site.
l
RPO seconds before the point of failure
l
Unlimited distance
See: Write operations in asynchronous mode on
page 127.
Primary
Secondary
Unlimited distance
Asynchronous
R1 R2
SRDF/Metro
Host or hosts (cluster) read and write to both R1
and R2 devices. Each copy is current and
consistent. Write conflicts between the paired
SRDF devices are managed and resolved.
Up to 125 miles (200 km) between arrays
See: SRDF/Metro on page 145.
SRDF links
Site A Site B
Multi-Path
R1
R2
SRDF links
Site A
Site B
R1
R2
Read/Write
Read/Write
Cluster
Read/Write Read/Write
SRDF/Data Mobility (SRDF/DM)
This example shows an SRDF/DM topology and the
I/O flow in adaptive copy mode.
l
The host write I/O is received in cache in Site A
l
The host emulation returns a positive
acknowledgment to the host
l
The SRDF emulation transmits the I/O across
the SRDF links to Site B
SRDF links
Site A Site B
Host
Remote replication solutions
SRDF 2-site solutions 103
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