cluster redundancy level (CRL) controls the number of recoverable failed instances in a shared-disk cluster. It is the maximum number of instances that can fail simultaneously while allowing recovery to proceed concurrently with other activity.
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Summary Information |
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|---|---|
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Default value |
1 |
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Valid values |
1 to n – 1, where n is the maximum number of instances specified in cluster.cfg or the quorum file. |
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Status |
Static |
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Display level |
Comprehensive |
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Required role |
System administrator |
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Configuration group |
Shared Disk Cluster |
If the number of failed instances exceeds the maximum number specified by the CRL, the cluster shuts down.
The value of maximum number of instances to a value that is equal to or less than the value of cluster redundancy level
The value of cluster redundancy level to a value equal to or greater than the value of maximum number of instances
When the cluster redundancy level value increases, so does the messaging traffic, as there are multiple copies of each lock in the cluster, and an increase in overhead required to maintain this redundancy level.
Other configuration parameters, such as number of locks and cache size need more resources for cluster redundancy level values greater than 1, which means you must increase max memory for the same number of locks value.
SAP recommends that you set cluster redundancy level to 1 if the failure of multiple instances is expected to be uncommon.