Table of ContentsView in Frames

Volume groups

A volume group is a set of drives that are logically grouped together by the controllers in a storage array. After you create a volume group, you can create one or more volumes in the volume group. A volume group is identified by the name you assign it when you create the volume group. If you do not name the volume group, it is identified by a sequence number that is defined by the controller firmware at volume group creation time.

Note: Some storage arrays permit different drive types in the same tray; however, you cannot have a combination of different drives in the same volume group.

To create a volume group, you must define the capacity and the RAID level.

Capacity is the size of the volume group. Capacity is determined by the number of drives that you assign to the volume group. You can use only unassigned drives to create a volume group. (Storage space on unassigned drives constitutes the unconfigured capacity of a storage array.)

Free capacity is a contiguous region of unassigned capacity in a designated volume group. Before you create a new volume in a volume group, you need to know the free capacity space so that you can determine the size of the volume.

The RAID level is the level of data protection that you want to define for your storage array. The RAID level that you choose affects storage capacity. When you configure your storage array, you must consider this compromise between data protection and storage capacity. In general, the more protection that you need, the less storage capacity is available in your storage array.

The following table lists the minimum number of drives and the maximum number of drives that you can use in a volume group based on the RAID level that you want to assign to the volume group.

RAID Level Minimum Number of Drives Maximum Number of Drives Redundancy
0 1 All. None
1, 10 2 All, if drive count is even; All - 1, if drive count is odd. Mirrored pairs
3 3 30 1 drive
5 3 30 1 drive
6 5 30 2 drives

You can determine the size of the volume group by multiplying the maximum number of drives in the volume group by the capacity of the smallest drive in the volume group.