Layered Volumes

Another Volume Manager virtual object is the layered volume. A layered volume is built on top of volume(s). The layered volume structure tolerates failure better and has greater redundancy than the standard volume structure. For example, in a striped and mirrored layered volume, each mirror (plex) covers a smaller area of storage space, so recovery is quicker than with a standard mirror volume. Figure 1-19 “Example of a Striped-Mirrored Layered Volume” shows an example layered volume design.

In Figure 1-19 “Example of a Striped-Mirrored Layered Volume”, illustrates how the volume and striped plex in the "User Manipulation" area allow you to perform normal Volume Manager tasks. User tasks can be performed only on the top-level volume of a layered volume. You cannot detach a layered volume or perform any other operation on the underlying volumes by manipulating the internal structure. You can perform all necessary operations from the user manipulation area that includes the volume and striped plex (for example, to change the column width, or to add a column).

The "Volume Manager Manipulation" area shows subdisks with two columns, built on underlying volumes with each volume internally mirrored. Layered volumes are an infrastructure within Volume Manager and they allow the addition of certain features to be added to Volume Manager. Underlying volumes are used exclusively by the Volume Manager and are not designed for user manipulation. The underlying volume structure is described here to help you understand how layered volumes work and why they are used by Volume Manager.

Figure 1-19 Example of a Striped-Mirrored Layered Volume

System administrators may need to manipulate the layered volume structure for troubleshooting or other operations (for example, to place data on specific disks). Layered volumes are used by Volume Manager to perform these tasks and operations: