Volume Management Terms

Volumes

A volume is a disk pack. A disk pack can be removable or nonremovable. The system recognizes a volume in a particular volume state. The volume state determines whether the volume is available or not. Volume states are described in chapter 3 of this manual.

Volume Sets

There are two types of volume sets, the system volume set and optional nonsystem volume sets. The system volume set is created when the operating system is installed and is always mounted when the system is operating. You can add extra volumes to the system volume set while the system is running. The system volume set contains two types of storage space, permanent and transient. Permanent space is used for files (permanent and temporary), label tables, and free space maps. Transient space is used for temporary data structures (stacks, heaps, and operating system data structures).

You create nonsystem volume sets when you want to restrict data for data accessibility, decrease the impact to system downtime (if a non-system volume is bad), or if you have to re-install the system. You can create and add extra volumes to nonsystem volume sets while the system is running. Nonsystem volume sets can be mounted on the system as needed and they contain only permanent space. If nonsystem volume sets are not defined on the system, all volumes will be part of the system volume set.

Table 2-1 “Differences between System and Nonsystem Volume Sets” lists the differences between the system volume set and nonsystem volume sets.

Nonsystem volume sets are also called user or mountable volume sets since they are not required for the system to run. You can remove (dismount) some or all of the volumes in a nonsystem volume set.

Types of Volumes

A volume set consists of two types of volumes, a master volume and optional member volumes. A volume set is created when the master volume is created. The master volume is the controlling volume of each set and must be present in order to access the set. The master contains the Volume Set Information Table (VSIT), the free space map, the file label table, and the root node of the accounting directory for the set. The VSIT is a table that contains information about all of the volumes and classes in the set. A member volume contains a volume label that identifies its volume set, a free space map, and a file label table.

Master Volumes

Table 2-2 “Master Volume Information” lists the information contained on the master volume of a volume set.

Table 2-2 Master Volume Information

Information	Description
volume label	Name of the master volume.
file label table	File labels for the files residing on the volume set.
free space map	Map of allocated and available disk sectors on the volume set.
directory root	Contains the directory of the volume set.
volume set's information table (VSIT)	Defines the volume set's configuration including volume set's name, names of the volumes and classes in the set, and the volumes in each class.
Files	User data.

 

The volume master of a nonsystem volume set is the only volume needed to define a volume set. When a master volume is mounted, the volume set is considered mounted. The master volume must be mounted before any file access can be made to other members of the volume set.

The master volume is created when you create a nonsystem volume set. It contains information about the set, including a root directory which enables the system to recognize the volume set.

The system master volume is initialized as LDEV 1. After the system is rebooted, additional volumes may be added online to the system volume set using the VOLUTIL utility described in chapter 3 of this manual. The master volume for the system volume set contains all the system files and system configuration information. It must be mounted for the system to boot or run.

Figure 2-2 A Master Volume

	NOTE: The master volume of a nonsystem volume set must be mounted for the system to recognize the volume set. The master volume of the system volume set must be mounted to boot the system.

Member Volumes

Member volumes can be added online after the volume set is created. They contain the information described in Table 2-3 “Member Volume Information”.

Table 2-3 Member Volume Information

Information	Description
Volume Label	Name of the member volume.
File Label Table	Contains the file labels for the files residing on the volume set.
Free Space Map	Map of allocated and available disk sectors on the volume set.
Files	User data.

 

Member volumes can belong to only one volume set since the root directory for their file information is contained on the master volume of the set.

Figure 2-3 A Member Volume

Volume Classes

A volume class is a subset of the volumes within one volume set. Volume classes are useful in restricting data to particular volumes in a volume set. Only the master volume and those particular volumes are needed to run applications. When data is restricted to a volume class, this limits the chance of losing data if a particular volume fails. Then problems on volumes outside that class, except the master volume, do not affect that data.

If resources are limited, more volumes can be defined in a set than there are physical drives to mount them. In this case, the volumes can be grouped into classes according to the types of information they contain. The volumes within a specific class can then be mounted as the data is needed.

Additionally, volume classes can be used to keep application programs on one drive and data on another, or to allow data to be mounted at different times.

	NOTE: When you create a new volume set, unless you specify another class, volume management assigns all volumes in the set to the default volume class, DISC.