Adjusting flow control in Veritas Volume Replicator (VVR) for Windows

Problem

Veritas Volume Replicator (VVR) uses a sliding-window algorithm to dynamically increase or decrease the amount of blocks that are sent from the primary to the secondary in response to network timeouts. In some environments, it is possible to improve performance by adjusting the algorithm.

Solution

Adjusting the sliding-window algorithm is done by setting the value of RPINCR and RPDECR.

Increasing these values causes VVR to be less aggressive at reducing throughput in response to network timeouts. However, setting these values too high may result in a large number of unacknowledged packets and resends, reducing throughput. The registry keys for RPINCR and RPDECR must be added manually, as DWORD values, to the following registry key:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\vxio\VVRParams

The default value for both RPINCR and RPDECR is 8. The values of RPINCR and RPDECR should both match. In addition, we recommend adjusting the values according to the following intervals: 8, 16, 24, 40, 60. These are decimal values.

A good first step would be to increase them the value to 16 and monitor the results.

Note: These changes must be made separately on all nodes.

Starting with Storage Foundation (SF) 5.1, you can use vxtune to make these changes

For example:

vxtune rp_incr_decr 16

Cycling the vxob or vxvm services (on all nodes) are required for this change to take effect. Further information on cycling these services can be found here:
http://www.symantec.com/docs/TECH51494
 


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