In either case r2 data is inconsistent until all the

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In either case, R2 data is inconsistent until all the invalid tracks are sent over. Therefore, it is advisable to enable SRDF/A after the two sides are completely synchronized. SRDF/Asynchronous Operations
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39 Copyright 2015 EMC Corporation. All rights reserved. In this example there is a workload on the devices in SRDF/A enabled state. A permanent loss of link places the devices in a Partitioned state. Production work continues on the R1 devices and the new writes arriving for the R1 devices are marked as invalid or owed to the R2. SRDF/A is dropped and session is Inactive. To get to this state, even the maximum DSE capacity should have been exceeded. So there is no choice but to drop SRDF/A. SRDF/Asynchronous Operations
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40 Copyright 2015 EMC Corporation. All rights reserved. When the links are restored, the pair state goes to Suspended. Even though the flags indicate SRDF/A mode, the session status is Inactive. Also note that R2 Data is Consistent. This is because the data would be consistent up to the last (N-M-2) Apply cycle. How ever there are accumulated R2 Invalid tracks that are owed to the R2 side. SRDF/Asynchronous Operations
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41 Copyright 2015 EMC Corporation. All rights reserved. As mentioned, we will next place the device group in Adaptive Copy Disk mode. As consistency was enabled when the links were lost, we have to first disable consistency before changing the mode to Adaptive Copy Disk. The RDF pair state is still Suspended. Next we resume the links. Once the RDF pair state goes to Synchronized, the mode can be changed to Asynchronous and consistency enabled. symrdf set mode async symrdf enable SRDF/Asynchronous Operations
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42 Copyright 2015 EMC Corporation. All rights reserved. Again, it is advisable to make a copy of the R2 prior to executing a failback operation. When workload is resumed on the R1 devices immediately after a failback, accumulated invalid tracks have to be synchronized from the R2 to the R1, and new writes must be shipped from the R1 to R2. If there is an interruption now, data on the R2 is not consistent. Even though SRDF/A can be enabled right after a failback, for reasons stated earlier, it should be enabled after the SRDF pairs entered the Synchronized state. SRDF/Asynchronous Operations
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43 Copyright 2015 EMC Corporation. All rights reserved. This lesson covered SRDF/A resiliency features such as Transmit Idle, Delta Set Extension, and Group-level Write Pacing. Method for recovering after a link loss was also discussed. SRDF/Asynchronous Operations
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44 Copyright 2015 EMC Corporation. All rights reserved. This lesson covers managing SRDF/A Multi-session Consistency. SRDF/Asynchronous Operations
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45 Copyright 2015 EMC Corporation. All rights reserved. Devices in RDF Group 20 are in an active SRDF/A session. The pair state is Consistent. The current cycle number for this group is 124.
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