Mapped Devices

• A Mapped Device is specified by a table that specifies a different target for different logical ranges of sectors.

• A target is an instance of a mapping such as: linear, striped, snapshot, mirror, error.

• The mapping tables are usually small. A btree structure holds the mapping from sector range to target. We know the entries in the btree in advance so we can build a very compact tree. The table lookup code is efficient and scales to large tables.

• Targets may be defined as separate modules which register with the Device Mapper, so third parties can invent new mapping methods (e.g. an alternative method of striping).