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42 Volume Groups
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 a sequence
number that is defined by the controller firmware when you created the volume group.
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. (In this programming guide, the 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.
Table 6 Maximum Number of Drives in a Volume Group Based on RAID Level
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.
RAID
Level
Minimum
Number of
Drives
Maximum
Number of
Drives
Redundancy
0 1 All None
1 1 All Mirrored pairs
3 3 30 1 drive
5 3 30 1 drive
6 5 30 2 drives