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Volume group creation

Volume groups are created from the total unconfigured capacity of a storage array. Total unconfigured capacity is the sum of the capacity of all the unassigned drives that are not in a disk pool or a volume group. A volume group can comprise several volumes. All volumes in a volume group use the same collection of drives and function at the RAID level configured for the volume group.

The storage management software provides a Create Volume Group wizard, which guides you through creating a volume group that comprises one or more drives in your storage array. When you create a volume group, you must specify two key parameters: the RAID level and the capacity. The RAID level defines how the data is organized, how redundancy is performed, and the minimum and maximum number of drives permitted in a volume group. The capacity is the sum of the capacity of the drives you select for your volume group.

Both the RAID level and the capacity settings for a volume group can be determined by the storage management software or entered manually. With the automatic method, you select the RAID level, and the storage management software automatically selects the best collection of drives for your volume group. With the manual method, you select the RAID level, and the appropriate type and number of drives to correspond to the selected RAID level. Whenever possible, use the automatic method.

After you create a volume group, the storage management software prompts you to create at least one volume. You must configure at least one volume in a volume group and map the volume to a host before the host operating system can save data to the volume on the volume group. If you do not configure a volume in your newly created volume group, the storage management software creates a free-capacity volume group. At some point, you must create volumes from the free capacity to enable the host operating system to save data to the volumes.

The limit on the number of volume groups is the number of drives supported by the storage array. This number varies with the different storage array models.

The following table provides the minimum and maximum number of drives that can be configured, based on RAID levels.

RAID Level Minimum number of drives Maximum number of drives Redundancy
0 1 All drives in a storage array None
10 2 All drives in a storage array Mirrored pairs
3 3 30 1 drive
5 3 30 1 drive
6 5 30 2 drives
Note: The table reflects RAID levels for volume groups, but not disk pools. You can find information about the number of drives required for disk pools in Disk pools or volume groups?.
Types of capacity

Available capacity in a volume group consists of these types of storage space:

The following figure shows a volume group that consists of three volumes and free capacity. One of the drives in the storage array has been configured as a hot spare drive that is available to a volume group in the storage array. The figure also shows the location of free capacity within the volume group and unconfigured capacity in the storage array.

Note: This is a stylized representation of storage because free and unconfigured capacity are spread across the entire drive, rather than in neatly organized blocks that physically reside in the same location.
1 Free Capacity within the Volume Group
2 Volume Group
3 Volume
4 Volume
5 Volume
6 Hot Spare Drive for all Drives within the Storage Array
7 Unconfigured Drive Capacity within the Storage Array

Volume group states

When a volume group is operational, the storage management software shows the status of the volume group.

Optimal – All drives in the volume group are present and the volume group has full redundancy, except for RAID 0 which has no redundancy.

Degraded – Enough drives in the volume group are present that data is accessible but redundancy has been reduced or completely lost.

Failed – Too few drives in a volume group are present in the storage array due with valid data, as a result of drive failure or removing a drive. The data in the volume is not accessible in this state.

Before creating volume groups, refer to the following online help topics in the Array Management Window: