HP Xw4400 - Workstation - 2 GB RAM Quick reference guide

HP Workstations RAID Primer
Mini White Paper
Introduction......................................................................................................................................... 2
Overview............................................................................................................................................ 2
RAID 0............................................................................................................................................ 2
RAID 1............................................................................................................................................ 2
RAID 5............................................................................................................................................ 2
RAID 10.......................................................................................................................................... 2

Introduction
RAID technologies are becoming a requested commodity across today’s workstations. This document
details some aspects of basic RAID levels.
Overview
RAID either stands for Redundant Array of Independent Disks or Redundant Array of Inexpensive
Disks. There are four basic RAID levels: 0, 1, 5 and 10. Over time, a number of other RAID levels
have been defined as well.
RAID was originally developed as a means to provide a degree of redundancy for disk data. It first
became popular in servers with SCSI drives where data reliability was important. Today, RAID can
be found across a number of different systems, including workstations, and a variety of drive types,
including IDE, SATA and SAS, as well as SCSI. RAID 0 was not in the original RAID proposal as it
didn’t technically meet the redundancy requirement. RAID 0 is now however considered as one of the
basic RAID levels which can be provided.
RAID 0
RAID 0 is often referred to as a Striped Disk Array, where the drives in the array are treated as one
large address space and successive data blocks are typically written to different drives in the array.
RAID 0 arrays are comprised of a minimum of two drives. Using RAID 0 has potential for improved
performance especially if drives are on different controllers.
RAID 1
RAID 1 is often referred to as a Mirrored Disk Array. A RAID 1 array is comprised of two drives.
Data blocks are written to both the first drive and the second. This allows for recovery from a single
catastrophic disk event. Typically performance is sacrificed for recoverability of data. Because data
is mirrored, half of the physical space is utilized.
RAID 5
RAID 5 is implemented as a combination of data striping with parity, where data and parity blocks
are written successively across the drives of the array. RAID 5 is used to ensure data integrity. This
RAID level requires a minimum of three drives. The effective disk availability of RAID 5 is the
equivalent of n-1 drives.
RAID 10
RAID 10 employs both mirroring and striping and may be implemented as a striped array which is
then mirrored, or a mirrored array which is then striped. Regardless of the implementation, this RAID
level takes a minimum of four drives. The effective disk availability is half of the physical disk space.
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RAID
Level Typical RAID Layout Description Advantages Disadvantages
RAID 0 D1[1] D1[2] D1[3]
D2[1] D2[2] D2[3]
D3[1] D3[2] D3[3]
D4[1] D4[2] D4[3]
A three drive RAID 0
configuration
Striped Disk Array – 2 or
more physical drives
Typically higher
performance
Lack of redundancy
implies that a single
disk failure is
unrecoverable
RAID 1 D1 D1
D2 D2
D3 D3
D4 D4
A two drive RAID 1
configuration
Mirrored Disk Array – 2
physical drives
More fault tolerant
than RAID 0
Typically slower
performance; half the
physical disk space is
used
RAID 5 D1[1] D1[2] D1[3] P1
D2[1] D2[2] P2 D2[3]
D3[1] P3 D3[2] D3[3]
P4 D4[1] D4[2] D4[3]
A four drive RAID 5
configuration
Striped Disk Array with
Parity – 3 or more
physical drives
Parity is employed to
ensure data integrity
Often difficult to
rebuild in case of a
disk failure
RAID 10 D1[1] D1[2] D1[1] D1[2]
D2[1] D2[2] D2[1] D2[2]
D3[1] D3[2] D3[1] D3[2]
D4[1] D4[2] D4[1] D4[2]
A four drive RAID 10 mirror of
stripes
Stripe of Mirrors or
Mirror of Stripes – 4 or
more physical drives
More fault tolerant
than RAID 0, similar to
RAID 1
High overhead and
high disk usage
© 2006 Hewlett-Packard Development Company, L.P. The information contained
herein is subject to change without notice. The only warranties for HP products and
services are set forth in the express warranty statements accompanying such
products and services. Nothing herein should be construed as constituting an
additional warranty. HP shall not be liable for technical or editorial errors or
omissions contained herein.
439276-001, October 2006
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