What is RAID?

[loganaustin662]

Hello,
Any one know about RAID.

Thanks.

[kevinchristian381]

RAID is Redundant Array of Independent (or Inexpensive) Disks. In fact, RAID is the way of merging multiple independent and relatively small disks into a single storage of a large size. RAID provides a way of storing the same data in different places.

The disks contained into the array are called array members. The disks can be combined into the array in different ways which are known as RAID levels. Each of RAID levels has its own characteristics.

How RAID is organized?

Two independent features are clearly decided in the RAID organization.

1. The organization of data in the array.
2. Implementation of each particular RAID installation - hardware or software.

RAID storage techniques

The main methods of storing data in the array are:

• Striping - splitting the flow of data into blocks of a certain size (called "block size") then writing of these blocks across the RAID one by one. This way of data storage concerns on the performance.
• Mirroring is a storage method in which the identical copies of data are stored on the RAID members simultaneously. This type of data placement offers the fault tolerance as well as the performance.
• Parity is a storage method which is utilized striping and checksum methods. In parity technique, a certain parity function is calculated for the data blocks. If a drive fails, the missing blocks are recalculated from the checksum, offering the RAID fault tolerance.

RAID levels

• RAID 0 - based on striping. This RAID level doesn't offer fault tolerance but increases the system performance (high read and write speed).
• RAID 1 - uses mirroring technique, increases read speed in some cases, and offers fault tolerance in the loss of no more than one member disk.
• RAID 0+1 - based on the combination of striping and mirroring techniques. This RAID level succeeds to RAID 0 performance and RAID 1 fault tolerance.
• RAID1E - utilizes both striping and mirroring methods, can survive a failure of one member disk or any number of nonadjacent disks. There are three subtypes of RAID 1E layout: near, interleaved, and far.
• RAID 5 - uses both striping and parity methods. Provides the read speed improvement as in RAID 0 approximately, survives the loss of one RAID member disk.
• RAID 5E - a variation of RAID 5 layout the only variation of which is an integrated spare space allowing rebuilding a failed array immediately in case of a disk failure.
• RAID 5 with delayed parity - similar to basic RAID 5 layout, but uses nonstandard scheme of striping.
• RAID 6 - similar to RAID 5 but uses two different parity functions.

RAID implementations

RAID can be generated by two different ways:

• Software RAID is the use of OS drivers.
• Hardware RAID is the use of special hardware, so called hardware RAID.

Software RAID

Software RAID is one of the economical RAID solutions.

Nowadays, almost of the OS has a built-in facility to create RAID, though not for all RAID levels. Thus, Windows home editions permit user to create only RAID 0, while RAID 1 and RAID 5 can be created only using Windows server editions.

There are certain limitations on the use of the software RAID to boot the system. Only RAID 1 can contain boot partition, while system boot is not possible with a software RAID 5 and RAID 0.

Most cases software RAID doesn't implement the hot-swapping and so it cannot be utilized where continuous availability is required.

Hardware RAID

Hardware RAID is created using separate hardware. Mainly there are two options:

• inexpensive RAID chip possibly built into the motherboard,
• More expensive option with a complex standalone RAID controller. Such controllers can be equipped with their own CPU, battery-backed up cache memory, and they typically support hot-swapping.

[charlottewatson505]

RAID (Redundant Array of Inexpensive Disks) is an collection of hard drives connected and setup in ways to help protect or speed up the performance of a computer's disk storage.

RAID is commonly used on servers and high performance computers.

[eeshathaker]

RAID stands for Redundant Array of Independent/Inexpensive Disks, and it allows you to store data across several hard drives. RAID is used to achieve data redundancy in order to reduce data loss and, in many circumstances, improve speed.

[mariaconcepcion1215]

RAID is a virtualization approach for data storage that combines many physical disc drive components into one or more logical units for data redundancy, performance gain, or both.