Alienware: What Is RAID?

Alienware: What is RAID?

Note: Please bookmark this article as restarts of the computer are recommended during the process to help resolve issues.

Applies to:

M17X R1, M17X R2, M17X R3, M17X R4, M18X R1, M18X R2 Laptops

Area-51, Aurora R1, Aurora R2, Aurora R3, Aurora R4 Desktops

Table of Contents:

1.      What is RAID?

2.      RAID levels

3.      How to create a RAID array?

This technology was defined in the late 1980’s by Patterson, Gibson and Katz at the University of California Berkeley, because of the dramatic increase in the amount of data that the computer information servers needed to store and the fact that storage technologies were getting too expensive. This technology was first published as "A Case for Redundant Arrays of Inexpensive Disks (RAID)". The basic idea of RAID was to combine multiple small, inexpensive disk drives into an array of disk drives which yields performance exceeding that of a Single Large Expensive Drive (SLED); this array of drives appears to the computer as a single logical storage unit or drive.

Now, the technology is known as Redundant Array of Independent Disks (RAID), and it is a way to virtualize multiple, independent hard disk drives into one or more arrays to improve performance, capacity and reliability (availability). RAID setups are mostly used in servers, but have recently been more regularly incorporated in high performance desktop and laptop computers.

RAID refers to the way the data is distributed in the disks attached to it. The same drives that are used in a RAID controller can be formatted, and used as independent drives if they are connected to non-RAID controllers.

	Note:
	The data saved in a disk by a RAID controller cannot be read by a different controller.

In this article, we are going to explain the most common RAID levels used on Alienware desktops and laptops.

1.       RAID 0: This is not technically a RAID, since it offers no redundancy or fault tolerance. In this level, data is striped across drives, the data is broken down into blocks and each block is written to a separate disk drive.

Advantages:

·         Input/ Output (I/O) performance is greatly improved by spreading the I/O load across many channels and drives.

·         Best performance is achieved when data is striped across multiple controllers with only one drive per controller.

·         No parity calculation overhead is involved.

·         Very simple design and easy to implement.

Disadvantages:

·         The failure of any disk in the array results in data loss.

 
Figure 1: RAID Level 0

 

	Note:
	RAID Level 0 requires a minimum of 2 drives to implement.

2.      RAID 1: Data is written identically to two drives, producing a "mirrored set"; at least two drives are required to constitute such an array.

Advantages:

·         One Write or two reads possible per mirrored pair

·         Twice the Read transaction rate of single disks, same Write transaction rate as single disks

·         100% redundancy of data means no rebuild is necessary in case of a disk failure, just a copy to the replacement disk

·         Transfer rate per block is equal to that of a single disk

·         Under certain circumstances, RAID 1 can sustain multiple simultaneous drive failures

·         Simplest RAID storage subsystem design

Disadvantages:

·         Typically the RAID function is done by system software, loading the CPU/Server and possibly degrading throughput at high activity levels. Hardware implementation is strongly recommended.

·         May not support hot-swap of failed disk when implemented in software mode.

Figure 2: RAID Level 1

	Note:
	For highest performance, the controller must be able to perform two concurrent separate Reads per mirrored pair or two duplicate Writes per mirrored pair. RAID Level 1 requires a minimum of 2 drives to implement.

3.      RAID 0+1: RAID level 0+1 uses a data-staging storage technique known as data parity. A RAID 0+1 array combines the high data access rate of a RAID level 0 array and the data protection (redundancy) of a RAID level 1 mirror by striping data across two drives and mirroring that striped data on a second set of two drives.

Advantages:

·         Increased performance

·         Data is fully redundant

Disadvantages:

·         Large number of drives required

·         Effective data capacity is halved

 
 
Figure 3: RAID Level 0+1

Striping
Mirroring

 

	Note:
	RAID Level 0+1 requires a minimum of 4 drives to implement. A minimum of 4 Hard Disk Drives are required to build a RAID 0+1 configuration.

  Click here to recreate a RAID configuration on your Alienware System