Raid 5 - Hitachi G1000 Hardware Manual

Description
Advantage
Disadvantage

RAID 5

A RAID 5 array group consists of four or eight drives (3D+1P) or (7D+1P).
The data is written across the four or eight drives in a stripe that has three or
seven data chunks and one parity chunk. Each chunk contains either eight
logical tracks (mainframe) or 768 logical blocks (open). This RAID 5
implementation minimizes the write penalty incurred by standard RAID 5
implementations by keeping write data in cache until the entire stripe can be
built, and then writing the entire data stripe to the drives. The 7D+1P RAID 5
configuration increases usable capacity and improves performance.
The following two figures illustrate the RAID 5 configurations. The tables
following the figures describes each configuration.
Note: There are two configurations of RAID 5: 3D+1P configuration (four
disk drives) and 7D+1P configuration (eight disk drives). The following
diagram shows the 3D+1P configuration. In the 7D+1P configuration, data is
arranged in the same way.
Hitachi Virtual Storage Platform G1000, G1500, and Virtual Storage Platform F1500 Hardware Guide
Item
Mirror disks (duplicated writing). The two parity groups of RAID 1(2D+2D) are
concatenated and data is distributed on them. In the each RAID pair, data is
written in duplicate.
This configuration is highly usable and reliable because of the duplicated data. It
has higher performance than the 2D+2D configuration because it consists of the
four RAID pairs.
Requires disk capacity twice as large as the user data.
Hardware architecture
Description
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