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Chapter 13. Metro Mirror options and configuration 135
The switch back is completed with one more sequence of a Metro Mirror Failover followed by
a Metro Mirror Failback operations, both given at the now-recovered production site.
Figure 13-1 summarizes the process.
Figure 13-1 Metro Mirror Failover and Failback sequence
In this manner, Metro Mirror Failover and Failback are dual operations. It is possible to
implement all site switch operations with two pairs of failover and failback tasks (one pair for
each direction).
The Metro Mirror Failover and Failback modes can be invoked from the DS Storage Manager
GUI, the DS Command-Line Interface (CLI), TSO commands, or using the ICKDSF utility.
We give an example of a Metro Mirror Failover and Failback sequence and how to control it in
16.2, “Failover and failback using TSO” on page 187.
Note: For a planned switch over from site (A) to site (B), and in order to keep data consis-
tency at (B), the application at site (A) has to be quiesced before the Metro Mirror Failover
operation at (B).
Alternatively, you can use the freezepprc and unfreezepprc commands. The same
consideration applies when switching back from site (B) to (A).
Primary site (A) Secondary site (B)
Normal operation
site (A) production site
site (B) recovery site
Updates are transferred
Source = A
full duplex
Target = B
full duplex
When planned/unplanned outage at (A):
At (B): Metro Mirror Failover
restart application processing
Establish with Failover
B full duplex
A full duplex
Establish with Failback
Source = B
suspended
Source = B
copy pending
Establish with Failover
Target = A
copy pending
Source = A
suspended
Establish with Failback
Source = A
full duplex
Target = B
full duplex
With site (A) recovered and operable.
At (B):
1. Metro Mirror Failback
2.
stop application processing
With pairs in full duplex.
At (A):
1. Metro Mirror Failover
2.
start application processing
3. Metro Mirror Failback