Overview

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With the Concentrated Dispersall feature, each Slicestor® device may be responsible for multiple slices of a given object stored in the system. Previously, each Slicestor device could only hold one slice of a given object. Prior to this the IDA Width set a lower bound on the number of Slicestor devices necessary in the deployment. For example, when using an IDA Width of 36, one would have to deploy at least 36 Slicestor devices. With the Concentrated Dispersal feature, each Slicestor device might hold 12 slices of each object, and so only 3 Slicestor devices would be necessary. By continuing to use a large IDA Width, high reliability and storage efficiency can be attained, but now with a much smaller hardware footprint.

Deploying a system requires the selection of an IDA Width, Threshold, and Write Threshold that provides an acceptable level of storage efficiency, reliability, and availability. Achieving good reliability requires a sufficient difference between Threshold and Write Threshold. A high write availability, similarly requires a sufficient difference between Width and Write Threshold. Finally, for the system to provide good storage efficiency requires the ratio between IDA Width and Threshold to be as small as possible while meeting the previous reliability and availability goals.
  • Initial deployments were expensive which precludes some customers with small data storage requirements from using dispersed storage.
  • It set a high lower-bound on the amount of usable storage capacity the system provides, and expands by. This made it difficult to support sub-PB systems efficiently.
  • It forces some customers with small numbers of Slicestor devices to compromise with either less reliable, or less efficient IDA configurations.

With Concentrated Dispersal, all of these problems are avoided. It enables systems on the order of a few hundred terabytes, while retaining the superb reliability and storage efficiency properties that previously could only be achieved in much larger systems comprised of dozens of devices.