RAID — Begin With The Basics

RAID — Begin With The Basics
How Does RAID Work?
RAID increases data protection and performance by
duplicating and/or spreading data over multiple disks.
What is RAID?
RAID stands for Redundant Array of Inexpensive Disks. RAID is a method of logically treating
several hard drives as one unit. It can offer fault tolerance and higher throughput levels than a
single hard drive or group of independent hard drives.
DRIVE 1
Mirroring
Mirroring & Striping
Duplicates data from primary
drive to secondary drive
Mirrors data that is striped, spread
DRIVE 2
evenly across multiple disks
Why Do We Need It?
RAID provides real-time data recovery when a hard drive fails, increasing system uptime and
availability while protecting against loss of data. Multiple drives working together also increase
system performance.
DRIVE 1
DRIVE 1
DRIVE 3
DRIVE 2
DRIVE 2
DRIVE 4
Levels of RAID
Minimum # of Drives
DRIVE 1
DRIVE 3
DRIVE 2
DRIVE 4
RAID Level
Description
Benefit
RAID 0
Data striping (no data protection)
2
Highest performance
RAID 1
Disk mirroring
2
Highest data protection
RAID 1E
Disk mirroring
3
Highest data protection for an odd number of disks
RAID 5
Data striping with distributed parity
3
Best cost/performance balance for multi-drive environments
RAID 5EE
Data striping with distributed parity with
hotspare integrated into the array
4
The cost/performance balance of RAID 5 without setting aside a dedicated hotspare disk
RAID 6
Data striping with dual distributed parity
4
Highest fault tolerance with the ability to survive two disk failures
RAID 10
Data striping of RAID 1 arrays
4
Highest performance with highest data protection
RAID 50
Data striping of RAID 5 arrays
6
Increased capacity and performance for multi-array RAID 5 environments
RAID 60
Data striping of RAID 6 arrays
8
Highest fault tolerance with the highest data protection
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Types of RAID Implementation
Glossary
Type
Description
Advantages
Ideal for
Softwarebased
Included in the operating system (OS), such
as Windows®, NetWare,
and Linux. All RAID
functions are handled
by the host CPU which
can severely tax its
ability to perform other
computations.
• Low price
Best used for large
block applications such
as data warehousing or
video streaming. Also
where servers have the
available CPU cycles to
manage the I/O intensive operations certain
RAID levels require.
Processor-intensive
RAID operations are
off-loaded from the
host CPU to enhance
performance. Batteryback write back cache
can dramatically
increase performance
while minimizing risk of
data loss.
• Data protection and
performance benefits
of RAID
Connects to the
servervia a standard
HBA or controller. RAID
functions are performed
on a microprocessor
located on the external
RAID controller independent of the host.
• OS independent
Hardwarebased
External
hardware
• Only requires a
standard HBA
• More robust faulttolerance features
and increased
performance
vs.software-based
RAID
Recommend Adaptec RAID Products
Adaptec by PMC delivers the industry’s most trusted RAID technology,
built on two decades of pioneering RAID leadership. We offer the
industry’s most advanced data protection, including RAID 0, RAID 1,
RAID 1EE, RAID 5, RAID 6, RAID 10, RAID 50, RAID 60, and
Copyback Hot Spare.
Best used for small
block applications such
as transaction oriented
databases and web
servers.
Copyback Hot Spare: When a failed drive is replaced, data is automatically copied from
the hot spare back to the replaced drive, allowing the hot spare to remain in the same spot.
Dual Drive Failure Protection (RAID 6, 60): Provides double redundancy and the
ability to sustain two drive failures. Data is striped across at least 4 physical drives
and a second parity scheme is used to store and recover data.
Fault Tolerance: The ability of a system to continue to perform its functions even when
one or more of its hard disk drives have failed.
Hot Spare: A spare hard drive which will automatically be used to replace a failed
member of a redundant disk array.
Hot Swap: The ability to replace a failed member of a redundant disk array with a good
drive without bringing down the server or interrupting transactions that involve the other
devices.
Mirroring (RAID 1): Provides data protection by duplicating all data from a prmary
drive onto a secondary drive.
Parity: A form of data protection used by RAID 5 to re-create the data of a failed drive.
RAID 0: See “Striping.”
RAID 1: See “Mirroring.”
RAID 1E: See “Striped Mirroring.”
Build high-capacity
storage systems for
high-end servers
RAID 5: Combines data striping (for enhanced performance) with distributed parity
(for data protection) to provide a recovery path in case of failure.
RAID 5EE: See “Hot Space.”
RAID 6: See “Dual Drive Failure Protection.”
RAID 10: Combines RAID 0 (data striping) and RAID 1 (disk mirroring).
RAID 50: Combines multiple RAID 5 sets with data striping (RAID 0) to increase
capacity and performance without adding disks to each RAID 5 array.
RAID 60: Combines multiple RAID 6 sets with data striping (RAID 0) to increase
capacity and performance without adding disks to each RAID 6 array.
Striped Mirror (RAID 1E): Combines data striping from RAID 0 with data mirroring
from RAID 1 to extend RAID 1 data availability across an odd number of disks.
Striping (RAID 0): Spreads data evenly over multiple drives to enhance performance.
Because there is no redundancy scheme, it does not provide data protection.
Hot Space (RAID 5EE): Provides the protection of RAID 5 and adds a hot spare disk to
the array. This extra drive enhances RAID 5 performance with higher I/Os per second.
For more information:
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