Swift uses zoning to isolate the cluster into separate partitions to isolate the cluster from failures. Swift data is replicated across the cluster in zones that are as unique as possible. A zone is an arbitrary grouping of nodes; typically zones are established that use physical attributes of the cluster, such as geographical locations, separate networks, equipment racks, storage subsystems, or even single drives. Zoning allows the cluster to tolerate equipment failures within the cluster without data loss or loss of connectivity to the remaining cluster.
By default, Swift replicates data 3 times across the cluster. Swift replicates data across zones in a unique pattern that attempts to ensure high availability and high durability for data. Swift chooses to place a replica of data in a server in an unused zone before placing it into an unused server in a zone that already has a replica of the data.
The inherent data integrity features built into FlashArrays ensures that clients always have access to their data - regardless of drive or other component failures within the storage subsystem. When FlashArray storage is used Swift data replication counts specified when rings are built can be reduced from 3 to 1.
In a cluster that contains several FlashArray systems zoning may be done through the use of 1 or more FlashArrays as a zone. An example of this is shown in Figure 8.2, “Controller-subsystem based zoning”.
Figure 8.2. Controller-subsystem based zoning