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Swarm continuously sends the nodes updates about the cluster's logical usage (the current number of objects and the space they consume), which the nodes update with the local space-affecting activity. Swarm then aggregates these updates (for accuracy) and publishes them via SNMP and REST as logicalObjects and logicalSpace. A third statistic, logicalUnprocessed, exists to provide insight into the accuracy of the other statistics (the closer to zero it is, the more accurate they are). Swarm propagates this data quickly, so there is little lag behind the cluster activity that affects usage: writes, deletes, and updates. After a disk failure, however, you will see a a drop in the aggregated estimates is seen, followed by an increase to the true value, once Volume Recovery recreates the lost streams that were previously on that the disk.
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TipWhen you first boot your booting the cluster after installing or upgrading to version 9.0, Swarm starts traversing the volumes to build these statistics, so they will are not be accurate until that completes; however, the value of |
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Aggregates | Units | Description | Accuracy | ||
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logicalObjects | count | The number of unique objects (including historical versions) stored for the entire cluster. Each content object counts only as 1, regardless of the number of replicas or EC segments that comprise it. | Approaches the actual number of logical objects in the cluster, minus context (domain, bucket) objects.
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logicalSpace | MB | The logical space stored for the entire cluster, including historical versions (which are separate objects). | Includes both the data and the persisted headers on each object, with header newlines counting as two characters (‘\r\n’). EC encoded objects may include a small overage. | ||
logicalUnprocessed | count | The number of streams in the cluster that have not been accounted for in After implementation, it will drop drops until it catches up, approaching zero. | When compared to the number of streams in the cluster, allows rough verification of other statistics, especially following the first boot after it is implemented. |
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Trends — Each volume in a Swarm cluster is computing partial statistics for logical objects with replicas on other volumes. Swarm works to keep the correct number of replicas (and EC segments) for every object, but, if there are too many replicas, the statistics will trend higher. In the case of hardware failure, the statistics will trend lower while the recovery is taking place.
Timing — Each volume has accurate partial statistics immediately after a write or delete. REST API statistics are immediately available after each volume broadcasts messages that are sent every 30 seconds, but SNMP adds up to another 60 seconds for periodic polling of the aggregated values. Metrics does not aggregate, so the periodic metrics reports will be is current with respect to the accounting cursor.
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