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Swarm has an Overlay Index, which provides increased scalability in a storage cluster. When enabled, the Overlay Index tracks object locations in a shared cluster-wide index, minimizing multicast traffic in the cluster network.
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By default, the Overlay Index is enabled for clusters with 3 or more nodes. the Overlay Index can be configured without rebooting the cluster by setting it as above in Cluster Settings or through its SNMP OIDs:
Overlay Settings | Default | SNMP OID | Description |
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index.optimize404 | TRUE | overlayOptimize404 | Optional. Enables the Optimize 404 feature in the overlay index, which returns 404 without multicast where possible. With the Overlay Index enabled and fully populated and Optimize 404 enabled, Swarm provides faster 404 (Not Found) responses for missing objects. |
index.overlayEnabled | TRUE | overlayIndexEnabled | Enables the overlay index. |
index.ovMinNodes | 3 | overlayMinNodes | Count. The minimum number of cluster nodes needed to activate use of the overlay index. |
Requirements
The Overlay Index provides these features:
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To support these features, the Overlay Index requires additional index slots in cluster node RAM to store the additional index information. The Overlay Index is not populated and the cluster continues to use multicast to locate objects if there are not enough nodes or RAM resources to hold the additional index information. Additional RAM must be added and the nodes rebooted to take advantage of the Overlay Index if the current node indexes are full.
See the Hardware Requirements for Storage for RAM requirements.
Determining
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Status
Check the value of the indexOverlayStatus SNMP OID to determine the current state of the Overlay Index at a given time. The status of the Overlay Index is one of the following:
Disabled: When the overlay is turned off.
Uninitialized: When the overlay is first activated.
Operational: When population of the Overlay Index is in process.
Authoritative: When the node servicing the SNMP query has determined the Overlay Index is fully populated for the entire cluster. The Optimize 404 feature only works when the Overlay Index is authoritative.
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