FICON

 

 

 

PPRC

ESS 750

ESS 800

FCP

 

 

Links

Global Copy

OR Metro Mirror

 

DS 6000

 

 

 

 

 

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.

260DS6000 Series: Concepts and Architecture

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IBM manual 260 DS6000 Series Concepts and Architecture