3.2. 卷组

物理卷合并为卷组（VG）。这样就创建了一个磁盘空间池，在它之外可分配逻辑卷。

Within a volume group, the disk space available for allocation is divided into units of a fixed-size called extents. An extent is the smallest unit of space that can be allocated. Within a physical volume, extents are referred to as physical extents.

逻辑卷会被分配成与物理卷扩展相同大小的逻辑扩展。因此卷组中逻辑卷的扩展大小都是一样的。卷组将逻辑扩展与物理扩展匹配。