The Logical Volume Manager is a subsystem for online disk storage management which has become a de facto standard for storage management under Linux.
a software tool that allows storage drive space to be added or expanded on the fly without system reboots or shutdowns, giving systems administrators more flexibility for operations
The subsystem used for managing disk storage. Logical volume management provides a higher-level abstraction of physical storage. A logical volume could arrange physical storage by the concatination, mirroring, or striping of physical storage for high availability and/or performance.