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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, Object Storage can
segregate the objects within a single cluster.
Storage policies can be used 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.
- A non-default storage policy is used only if specified when creating
a container, using the X-Storage-Policy: <policy-name> header.
After the container is created, it uses the created storage policy.
Other containers continue using the default or another storage policy
specified when created.
For more information about storage policies, see: Storage
Policies