Swift Ring Considerations with DDP

A Swift ring represents a mapping between the names of entities stored on disk and their physical location. There are separate rings for accounts, containers, and objects. When other components need to perform any operation on an object, container, or account, they need to interact with the appropriate ring to determine its location in the cluster.

The ring maintains this mapping using zones, devices, partitions, and replicas. Each partition in the ring is replicated 3 times, by default, across the cluster. The locations for a partition are stored in the mapping maintained by the ring. The ring is also responsible for determining which devices are used for handoff in failure scenarios.

	Tip
	When leveraging the DDP capabilities of the E-Series storage system, it is only necessary to have Swift maintain 1 replica of the data as the storage subsystem automatically is providing sufficient replication of the data within the storage cluster to withstand multiple failures.

The number of replicas for partitions within Swift rings is set at the time the ring is created. To create the Swift rings for the Swift object types of account, container, and object, use the swift-ring-builder CLI command with the replicas parameter set to 1:

#swift-ring-builder ring-name create part-power replicas min-hours
swift-ring-builder account.builder create 10 1 1
swift-ring-builder container.builder create 10 1 1
swift-ring-builder object.builder create 10 1 1
    

Tip

When creating the Swift rings, the number of partitions per ring must be calculated. However, the default computation for computing the number of partitions (expressed by the exponent of 2) - otherwise known as the partition power (part-power) - is based on the number of disks in a Swift cluster. While some Swift deployments (without NetApp E-Series storage solutions) utilize direct attached storage without RAID, with E-Series virtual disks are attached and leveraged that are created from a dynamic disk pool. As such, be sure to calculate the partition power as a function of the virtual disk count, rather than the number of physical (spinning or SSD) drives present.