24 Nov 08 RAID – Redundant Array of Inexpensive Disks

RAID – Redundant Array of Inexpensive (or sometimes “Independent”) Disks – is a method of combining several hard drives into one logical unit. It can offer fault tolerance and higher throughput levels than a single hard drive or group of independent hard drives.

RAID is a mature technology that speeds up data access while at the same time protecting your data from hard disk failure. RAID is quickly becoming a necessary component in every network since data loss and downtime can prove both fatal and financially destructive. Most networks are designed to provide instant access to massive amounts of data. More and more employees have to access customer and other databases. Intranets and corporate Web sites provide access to huge databases online.

RAID provides increased storage capacities, and protects your important data from hard drive failure.

RAID Levels:

• RAID 0
• RAID 1
• RAID 3
• RAID 5
• RAID 10

There are multiple benefits of using RAID:

• Reliability
• Scalability
• Real-time data recovery with uninterrupted access when a hard drive fails
• System uptime and network availability
• Protection against data loss
• Multiple drives working in parallel increase system performance

A disk system with RAID capability can protect its data and provide on-line, immediate access to its data, despite a single disk failure (some RAID storage systems can withstand two concurrent disk failures). RAID capability also provides for the on-line reconstruction of the contents of a failed disk to a replacement disk.

RAID offers faster hard drive performance and nearly complete data safety. Storage requirements are expanding as file sizes get bigger and rendering needs get more complex. If you handle very large images or work on audio and video files, faster data throughput means enhanced productivity. RAID can be backed up to tape while the system is in use.

NT offers native support for software-based redundant arrays of inexpensive disks (RAID). RAID is a drive configuration that uses multiple drives to provide higher speed and greater data protection than a single drive. NT can combine multiple independent drives into a RAID configuration through its disk subsystem components. In other words, NT performs all of the complicated disk read and write activities necessary to create RAID sets. This is known as software-based RAID. It has the advantage of being cheap, because it is built into Windows NT. However, it is minimally useful as a performance improvement tactic. NT provides RAID from software by using the CPU and other system resources to process disk reads and writes. For systems with minimal disk access, performance is improved; however, for systems with significant disk access, performance is severely degraded.

Hardware RAID devices are specialty drive devices that host multiple drives external to the computer system. Hardware RAID devices manage all of the disk reads and writes independent of the operating system. This provides several benefits, including true high-performance disk access. Hardware RAID does not tax the CPU or other system resources because a hardware RAID device requires no more processing power than a standard disk drive. In fact, the OS is typically unaware that the disk device is RAID hardware. The only drawback to hardware RAID is the cost. A RAID device typically costs two to ten times as much as a comparable non-RAID drive (or set of drives).

There are 5 most commonly used RAID levels. These levels are not ratings, but rather classifications of functionality. Different RAID levels offer dramatic differences in performance, data availability and data integrity depending on the specific I/O environment. There is no single RAID level that is perfect for all users.