Volumes

Various software packages are available in the industry that are either generically known as Volume Manager technology or Software*RAID (Redundant Arrays of Independent Disks) technology. These technologies are deployed to improve the RAS (Reliability, Availability, and Scalability) characteristics of the underlying storage. For example, Veritas Volume Manager is a popular product used across multiple operating systems. Such technologies are referred to as Volumes in Enterprise Manager.

The Volumes option displays the allocated and unallocated storage space for all the entities present in the Volumes layer, including relevant attributes for the underlying Volumes layer technology.

Types of Entities

The Volumes layer can have entities of various types present internally. Entity type shown in Enterprise Manager is based on the terminology as defined by the deployed Volumes layer technology. For example, a Veritas volume manager defines and supports the following entity types: Volume, Plex, Sub Disk, VM Disk, VM Spare Disk, and Diskgroup. Refer to the vendor documentation for more details about the Volumes technology deployed on your system.

Top-Level Entities

Top-level Volumes layer entities provide storage space to the upper layers for usage. If a top-level entity does not have an association to an entity from an upper layer, the top-level entity is unallocated and it is available for further allocation related activity.

For each vendor technology, entities of specific types from their layer can be associated with entities from the upper layers. File Systems, Databases, and ASM are examples of upper layers. For example, entities of type 'Volume' in Veritas Volume Manager are such entities. These entities are referred to as top-level Volumes layer entities in this documentation.

Bottom-Level Entities

For each vendor technology, entities of specific types from their layer can be associated with entities from the disk layer. For example, VM Disk and VM Spare Disk entities in Veritas Volume Manager are such entities. These entities are considered to be bottom-level Volumes layer entities in this documentation.

Bottom-level Volumes layer entities consume storage space from the disk layer and provide storage space to the rest of the entities in the Volumes layer. Bottom-level entities of 'reserve' or 'spare' type are always allocated and no space is available from them for allocation purposes. Note that spare entities are utilized by the Volumes technology for handling disk failures and they are not allocated to other entities present in the Volumes layer by way of administrator operations.

Non-spare bottom-level entities can have an association to an intermediate or top-level entity configured using respective vendor administration utilities. If no association exists for a non-spare bottom-level entity, then it is unallocated. If one or more associations exist for the non-spare bottom-level entity, then the space consumed through the existing associations is allocated. It is possible that some space could be left in the bottom-level entity even if it has some associations defined for it.

Storage space in non-spare bottom-level entities not associated with intermediate or top-level entities is available for allocation and it is accounted as unallocated space in the bottom-level entity.

Intermediate Entities

Non top-level and bottom-level entities are considered to be intermediate level entities of the Volumes layer. For example, Volume (layered-volume case), Plex and Sub Disk entities in Veritas Volume Manager are such entities.

If an intermediate entity has association to another intermediate or top-level entity, the storage space consumed through the association is allocated. Space present in the intermediate entity that is not consumed through an association is unallocated.

The following vendor products are instrumented:

Platform	Product
Solaris	Solaris Volume Manager
Linux	mdadm, raidtool, Suse LVM