IBM System Storage N Series Implementation of RAID Double Parity for Data Protection

An IBM Redpaper publication

Published 12 April 2006, updated 06 October 2009

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IBM Form #: REDP-4169-00
(22 pages)

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Authors: Chrisanthy Carlane, Alex Osuna


This IBM Redpaper discusses the implementation of RAID double parity in IBM System Storage N series.

The following topics are covered:
- The need for RAID-DP
- How RAID-DP works
- Protection levels with RAID-DP

To date, RAID technology, with its single parity, offered protection from a single failed disk with the caveat that no other disk fail or, increasingly more likely as disk media grow larger, an uncorrectable bit error would not occur during a read operation, while reconstruction of data lost on the failed disk was still in progress. If either secondary event occurs during reconstruction, then some or all data contained in the RAID array could be lost.

IBM Storage System N series introduces double-parity RAID, named RAID-DP. This document provides an overview of RAID-DP and how it dramatically increases data fault tolerance from various disk failure scenarios. Other key areas covered include how much RAID-DP costs, special hardware requirements, and converting from existing RAID4-based volumes to RAID-DP. This document presents a double-disk failure recovery scenario to show how RAID-DP both allows the volume to continue serving data and recreates data lost on the two failed disks.

Table of contents

The need for RAID-DP
How RAID-DP works
Protection levels with RAID-DP

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