What is RAID?

• RAID stands for Redundant Array of Inexpensive (or sometimes "Independent") Disks.
• RAID is a method of creating one or more pools of data storage space from several hard drives.
• It can offer fault tolerance and higher throughput levels than a single hard drive or group of independent hard drives.
  

The Benefits of RAID?

• Reliability: Provides real-time data recovery with uninterrupted access when a hard drive fails
• Increases system uptime and network availability
• Protects against data loss
• Performance
• Multiple drives working in parallel increase system performance

The Types Of RAID

	Software-based RAID	Hardware-based RAID	External Hardware RAID

Description	Included in OS's 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	Processor-intensive RAID operations are off-loaded from the host CPU to enhance performance.	Connects to the server via a standard controller. RAID functions are performed on a microprocessor located on the external RAID controller independent of the host.
Advantages	Low price Only requires a standard controller	Data protection and performance benefits of RAID More robust fault-tolerant features and increased performance versus software-based RAID.	OS independent Build super high-capacity storage systems for high-end servers.

 

The Levels of RAID

	RAID 0	RAID 1	RAID 10 (also known as RAID 0/1)	RAID 5	RAID 50 (also known as RAID 0/5)
Description	Data striping (no data protection)	Disk mirroring	RAID 0 and RAID 1 combined	Data striping with distributed parity	RAID 0 and RAID 5 combined
Minimum # of Drives	Two	Two	Four	Three	Six
Benefit	Highest performance	Data protection through redundancy	Highest performance with data protection	Best balance of cost/ performance/ data protection	Provides increased fault tolerance

 

Technology Comparison

	ATA	Serial ATA	SCSI

Best Suited For	IDesktop and low-end workstations perform other computations	Sub-entry to entry-level servers and high-end workstations	Low- to high-end server when scalability is desired
Advantages	Uses low-cost ATA drives	Performance: up to 150 MByte/sec Thin cabling to simplify and improve airflow	Performance: up to 320 MByte/sec Reliability Connectivity to the largest variety of peripherals Expandability

 

Glossary

Array -- Two or more hard disk drives grouped together to appear as a single device to the host computer.

ATA -- Acronym for "AT Bus Attachment"– a standard interface for IDE devices

Bootable Array Support -- The ability to make the system boot from a RAID array instead of from a standalone (single) disk.

Cache -- A temporary, fast storage area that holds data from a slower storage device for quick access. Cache storage is normally transparent to the accessing device.

Fault Tolerance -- The ability of a system to continue to perform its functions even when one or more hard disk drives have failed.

Hot Spare -- A spare hard drive which will automatically be used to replace the failed member of a redundant disk array.

Hot Swap -- The ability to remove a failed member of a redundant disk array and replace it with a good drive without bringing down the server or interrupting transactions that involve other devices.

Microprocessor -- A processor on the RAID card which performs all RAID management functions.

Mirroring (RAID 1) -- Provides data protection by duplicating all data from a primary drive on a secondary drive.

OS -- Operating System

Online Capacity Expansion (O.C.E.) -- A process for adding storage capacity to an existing RAID array without having to take the server offline.

Optimized Disk Utilization -- Allows the full available capacity to be used on all drives attached to a controller, even if the drive sizes are different.

Parity -- A form of data protection used by RAID level 5 to recreate the data of a failed drive in a disk array.

RAID Levels -- RAID levels refer to different array architectures that offer various advantages in terms of data availability, cost, and performance.

RAID Level Migration -- A process to change the RAID level of an existing RAID array without taking the server offline. Also known as Morphing.

RAID 0 -- See "Striping"

RAID 0/1 -- Combines RAID 0 (data striping) and RAID 1(disk mirroring).

RAID 1 -- See "Mirroring"

RAID 5 -- Combines data striping (for enhanced performance) with distributed parity (for data protection) to provide a recovery path in case of disk drive failure.

RAID 50 -- Combines multiple RAID 5 sets with RAID 0 (striping).

RAID Management Software -- Software that makes installation, configuration, and management of RAID arrays easy. Often includes features such as e-mail notification and remote management.

SCSI -- Acronym for "Small Computer System Interface". SCSI is the technology that allows you to connect various devices to your PC. This connection is made using a SCSI card that fits inside your computer.

Serial ATA -- The next generation ATA interface

Striping (RAID 0) -- Spreads data evenly over multiple drives to enhance performance. Because there is no redundancy scheme, it does not provide data protection.