A subdisk is a set of contiguous disk blocks. A block is a unit of space on the disk. VxVM allocates disk space using subdisks. A VM disk can be divided into one or more subdisks. Each subdisk represents a specific portion of a VM disk, which is mapped to a specific region of a physical disk.

The default name for a VM disk is diskgroup## and the default name for a subdisk is diskgroup##-##, where diskgroup is the name of the disk group to which the disk belongs.

Figure: Subdisk example shows disk01-01 is the name of the first subdisk on the VM disk named disk01.

A VM disk can contain multiple subdisks, but subdisks cannot overlap or share the same portions of a VM disk. To ensure integrity, VxVM rejects any commands that try to create overlapping subdisks.

Figure: Example of three subdisks assigned to one VM Disk shows a VM disk with three subdisks, which are assigned from one physical disk.

Any VM disk space that is not part of a subdisk is free space. You can use free space to create new subdisks.