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304 DS8000 Series: Concepts and Architecture
impact to the application write I/Os at 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 Metro 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 Metro 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 14-6.
Figure 14-6 Check with Global Copy whether all data replicated to the new volume
This approach is not really practical. ICKDSF allows you to query the status of a Global Copy
primary volume and displays the amount of data which is not yet replicated, as shown in
Example 14-2.
Example 14-2 Check through ICKDSF query commands that all data is replicated
PPRCOPY DDNAME(DD02) QUERY
ICK00700I DEVICE INFORMATION FOR 6102 IS CURRENTLY AS FOLLOWS:
PHYSICAL DEVICE = 3390
STORAGE CONTROLLER = 2105
STORAGE CONTROL DESCRIPTOR = E8