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Storage policies
Storage policies allow segmenting the cluster for various purposes through the creation of multiple object rings. Using policies, different devices can belong to different rings with varying levels of replication. By supporting multiple object rings, swift can segregate the objects within a single cluster.
Use storage policies for the following situations:
- Differing levels of replication: A provider may want to offer 2x replication and 3x replication, but does not want to maintain two separate clusters. They can set up a 2x policy and a 3x policy and assign the nodes to their respective rings.
- Improving performance: Just as solid state drives (SSD) can be used as the exclusive members of an account or database ring, an SSD-only object ring can be created to implement a low-latency or high performance policy.
- Collecting nodes into groups: Different object rings can have different physical servers so that objects in specific storage policies are always placed in a specific data center or geography.
- Differing storage implementations: A policy can be used to direct traffic to collected nodes that use a different disk file (for example: Kinetic, GlusterFS).
Most storage clusters do not require more than one storage policy. The following problems can occur if using multiple storage policies per cluster:
- Creating a second storage policy without any specified drives (all drives are part of only the account, container, and default storage policy groups) creates an empty ring for that storage policy.
- Only use a non-default storage policy if specified when creating a
container, using the
X-Storage-Policy: <policy-name>header. After creating the container, it uses the storage policy. Other containers continue using the default or another specified storage policy.
For more information about storage policies, see: Storage Policies