The order of write operations must be maintained within a group. Therefore, these out of order requests must be stored in memory on the secondary host until the missing request comes in and completes.
The secondary host can store up to the
The most common symptom of secondary memory exhaustion is the volume sets changing to logging mode. The RPC requests fail when memory is low. To avoid the problem, change the number of asynchronous threads for some of the groups from the default of two to one. This forces the earlier version 3.1 behavior with no extra memory requirement on the secondary host.
The need for extra memory is most common with large I/O on a high latency link. When selecting groups to use a single thread, your best choices are those groups with a good network connection. Such groups are most likely to fill the secondary queue and they derive the least benefit from multiple threads.
Users upgrading from Sun StorEdge Availability Suite 3.1 software must be aware that the default number of asynchronous threads is two, not one.
Chapter 2 Remote Mirror Software Troubleshooting Tips 17