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| Replicator Log overflow protection - srlprot attribute | ||
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| Prev | Measures to protect log overflow and replication latency | Next |
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| Replicator Log overflow protection - srlprot attribute | ||
|---|---|---|
| Prev | Measures to protect log overflow and replication latency | Next |
Volume Replicator provides the following modes of overflow protection: Override, Fail, DCM, and AutoDCM. You can also turn off the Replicator Log overflow protection feature by setting the attribute to off.
If the network is down or the Secondary is unavailable, the number of writes in the Replicator Log waiting to be sent to the Secondary could increase until the Replicator Log fills up. When the Replicator Log cannot accommodate a new write without overwriting an existing one, the condition is called Replicator Log overflow. The new writes are held up, DCM is activated, or the Replicator Log overflows depending on the srlprot setting.
Circumstances that can cause the Replicator Log to overflow when you replicate in the asynchronous mode are as follows:
A temporary burst of writes, or a temporary congestion in the network, causing the current update rate to exceed the currently available bandwidth between the Primary and the Secondary.
A temporary failure of the Secondary node or the network connection between the Secondary and the Primary.
An administrator pauses the RLINK from the VEA GUI or by executing a vxrlink pause command.
Inability of the network bandwidth to keep up with the update rate at the Primary on a sustained basis. This is not a temporary condition and can be corrected only by increasing the network bandwidth or reducing the application update rate, if possible.
If the Replicator Log overflows, the Secondary becomes out-of-date and must be completely synchronized to bring it up-to-date with the Primary. The Replicator Log protection feature of Volume Replicator enables you to either prevent the Replicator Log from overflowing or tracks the writes using Data Change Map (DCM) in the case of Replicator Log overflow. You must weigh the trade-off between allowing the overflow or affecting the application. You can prevent Replicator Log overflow by using the srlprot setting.
Volume Replicator provides the following modes of Replicator Log overflow protection: AutoDCM, DCM, Override, and Fail. These modes are activated only when the Replicator Log is about to overflow. You can set up Replicator Log protection by setting the srlprot attribute of the corresponding RLINKs to AutoDCM, DCM, Override, or Fail. You can turn off the Replicator Log protection by setting the srlprot attribute to off.
The following table describes the effect of the RLINK state on the Replicator Log protection.
Table: Effect of RLINK state on the Replicator Log Protection
Note: |
When srlprot=off, the Replicator Log overflows irrespective of whether the RLINK is connected or disconnected. |
If the Replicator Log overflow protection is enabled and if a write is about to cause the log to overflow, then the Replicator Log protection is turned on.