IBM System storage DS6000 Series, Redbooks

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DS6000 Series: Concepts and Architecture
Figure 13-5 Metro Mirror or Global Copy from ESS 750 or ESS 800 to DS6800
Metro Mirror (Synchronous PPRC) provides data consistency at any time once the volumes
are in full DUPLEX state, although through its synchronous approach it imposes a slight
impact to the application write I/Os to the source storage subsystems from where we migrate
the data. This assumes a local data migration and that the distance is within the supported
Metro Mirror distance for PPRC over FCP links. You can switch the application I/Os any time
from the old to the new disk configuration. This requires you to quiesce or shut down the
application server and restart the application servers after terminating the PPRC
configuration. The restart uses a modified I/O definition file but the volume serial number will
stay the same and all data will be located correctly through catalog locate processing.
Global Copy (PPRC-XD) on the other side does not impact the application write I/Os due to
its asynchronous data replication, but the drawback here is that it does not guarantee data
consistency at the receiving site. Before switching from the source equipment to the new
target equipment, make sure all data is replicated to the receiving site. This can be forced by
dynamically switching from Global Copy to Global Mirror. When all primary volumes are in full
DUPLEX state the source and target disk servers contain the same data at any time. At this
point prepare and execute the switchover to the new disk storage server.
Instead of switching from Global Copy to Global Mirror, you might stop the applications and
shut down the application servers. Then check that all data is replicated to the target disk
server. This might be a bit labor-intensive in a large environment without the help of
automation scripts. Basically you would check each individual primary volume (=source
volume) that all data is copied over. Through the current Copy Servers application on an ESS
800 this would look like Figure 13-6 on page 261.
PPRC
Links
FCP
Metro Mirror
ESS 750
Global Copy
ESS 800
OR
FICON
DS 6000