What is MetaLUN?

Posted by Diwakar

A metaLUN is a type of LUN whose maximum capacity can be the combined capacities of all the LUNs that compose it. The metaLUN feature lets you dynamically expand the capacity of a single LUN (base LUN) into a larger unit called a metaLUN. You do this by adding LUNs to the base LUN. You can also add LUNs to a metaLUN to further increase its capacity. Like a LUN, a metaLUN can belong to a Storage Group, and can participate in SnapView, MirrorView and SAN copy sessions. MetaLUNs are supported only on CX-Series storage systems.
A metaLUN may include multiple sets of LUNs and each set of LUNs is called a component. The LUNs within a component are striped together and are independent of other LUNs in the metaLUN. Any data that gets written to a metaLUN component is striped across all the LUNs in the component. The first component of any metaLUN always includes the base LUN. The number of components within a metaLUN and the number of LUNs within a component depend on the storage system type. The following table shows this relationship:
Storage System Type LUNs Per metaLUN Component Components Per metaLUN
CX700, CX600 32 16
CX500, CX400 32 8
CX300, CX200 16 8
You can expand a LUN or metaLUN in two ways — stripe expansion or concatenate expansion. A stripe expansion takes the existing data on the LUN or metaLUN you are expanding, and restripes (redistributes) it across the existing LUNs and the new LUNs you are adding. The stripe expansion may take a long time to complete. A concatenate expansion creates a new metaLUN component that includes the new expansion LUNs, and appends this component to the existing LUN or metaLUN as a single, separate, striped component. There is no restriping of data between the original storage and the new LUNs. The concatenate operation completes immediately.
During the expansion process, the host is able to process I/O to the LUN or metaLUN, and access any existing data. It does not, however, have access to any added capacity until the expansion is complete. When you can actually use the increased user capacity of the metaLUN depends on the operating system running on the servers connected to the storage system.


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