Vsp G1000, Vsp G1500, And Vsp F1500 Raid Implementation; Array Groups And Raid Levels - Hitachi G1000 Hardware Manual

VSP G1000, VSP G1500, and VSP F1500 RAID
implementation
The benefits of RAID technology are low cost, high reliability, and high I/O
performance of data storage devices. To gain these benefits, this storage
system supports RAID levels 1, 5 and 6. The features of the levels of RAID
technologies are described below.

Array groups and RAID levels

An array group (also called parity group) is the basic unit of storage capacity
for the storage system. In RAID 1, an array group is a set of four physical
drives where one drive is installed in the same location in each of four
contiguous disk trays in the same drive chassis. The following figure shows
part of a SFF drive chassis where two RAID 1 array groups are set up. RAID
group 1 consists of the drives highlighted by yellow rectangles. RAID group 2
is shown by the red rectangles.
In the above figure, the drives with the red rectangles are unformatted
physical drives so they are called an array group. The drives with the yellow
rectangles have been formatted as a RAID level and have initial parity data
on them, so they are called a parity group. Generally, this technical
distinction is often lost, and the terms parity group and array group are often
used interchangeably.
The storage system supports the following RAID levels: RAID 1, RAID 5, and
RAID 6. When configured in four-drive RAID 5 parity groups (3D+1P),
seventy-five percent of the raw capacity is available to store user data, and
twenty-five percent of the raw capacity is used for parity data.
Hitachi Virtual Storage Platform G1000, G1500, and Virtual Storage Platform F1500 Hardware Guide
Figure 10 RAID group example
Hardware architecture 53