Extents are contiguous blocks on the hard disk that are used to keep files close together and prevent fragmentation. Fragments occur when parts of a file are scattered across a hard disk and do not exist in contiguous blocks.

What are LVM extents?

LVM breaks up each physical volume into extents. A logical volume consists of a set of extents. Each extent is either wholly unused, or wholly in used by a particular logical volume: extents cannot be subdivided. Extents are the elementary blocks of LVM allocation.

What is an extent in a file system?

In computing, an extent is a contiguous area of storage reserved for a file in a file system, represented as a range of block numbers, or tracks on count key data devices. A file can consist of zero or more extents; one file fragment requires one extent.