A layered volume is constructed by mapping its subdisks to underlying volumes. The subdisks in the underlying volumes must map to VM disks, and hence to attached physical storage.
Layered volumes allow for more combinations of logical compositions, some of which may be desirable for configuring a virtual device. Because permitting free use of layered volumes throughout the command level would have resulted in unwieldy administration, some ready-made layered volume configurations are designed into VxVM.
See Layered volumes.
These ready-made configurations operate with built-in rules to automatically match desired levels of service within specified constraints. The automatic configuration is done on a "best-effort" basis for the current command invocation working against the current configuration.
To achieve the desired storage service from a set of virtual devices, it may be necessary to include an appropriate set of VM disks into a disk group, and to execute multiple configuration commands.
To the extent that it can, VxVM handles initial configuration and on-line re-configuration with its set of layouts and administration interface to make this job easier and more deterministic.