RAID (Redundant Array of Independent Disks) technology was invented in 1987 to improve data storage performance and reliability. It combines multiple disk drive components into one or more logical units. There are different RAID levels that determine how disk arrays are used, with RAID 0 through RAID 6 being the standard levels. RAID levels use techniques like striping, mirroring, and parity to provide features like fault tolerance, high throughput, and data redundancy. Each level has advantages and disadvantages for performance, reliability, and capacity.

1. RAID Technology
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2. Contents
 History
 Introduction
 Overview
 Standard Levels
 RAID 0
 RAID 1
 RAID 2
 RAID 3
 RAID 4
 RAID 5
 RAID 6
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3. HISTORY
 In 1987, invented by David Patterson, Garth A. Gibson, and Randy Katz at
the University of California, Berkeley.
 Stands for Redundant Array of Inexpensive Disks.
 A paper presented in June 1988 on "A Case for Redundant Arrays of
Inexpensive Disks (RAID)" at SIGMOD (Association for Computing
Machinery's) conference. In which they claimed that an array of cheap drives
that had been created for the growing personal computer market could beat
output on the top-performing mainframe disc drives of the time.
 While failures would increase in proportion to the number of drives, the
reliability of an array might far surpass that of any large single drive by
configuring it for redundancy.
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4. INTRODUCTION
 used to improve the performance and reliability of data storage
 Stands for Redundant Array of Independent Drives or Redundant Array of
Inexpensive Disks.
 connect two or more secondary storage devices or drives working in parallel
and use them as a single storage media.
 In order to accomplish various objectives, RAID consists of an array of discs in
which several discs are linked together. RAID levels determine how disc arrays
are used.
 Finally, For the purposes of data replication, performance enhancement, or
both, RAID is a data storage virtualization technology that incorporates several
physical disc drive components into one or more logical units.
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5. TYPES
RAID can be deployed by storage managers as
 hardware (controller card or chip) or
 software (software-only or hybrid)
 Hardware RAID:
 supported by a dedicated hardware controller
 can be executed by IT in two ways
 An external RAID Controller Card or
 An internal RAID-on-Chip
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6.  RAID Controller Card:
 Attaches to a PCIe or PCI-X motherboard slot with this plug-in expansion
card.
 A RAID processor and I / O processors with drive interfaces are included
in the card.
 The cards are costly, but all RAID operations are offloaded from the CPU
to the dedicated card, because they are independent of the host.
 RAID-on-Chip:
 The host interface, I / O interfaces for HDDs, the RAID processor and a
memory controller are combined into a single chip on the motherboard.
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7. Software RAID
 provides the host's RAID facilities
 comes in two flavors:
 pure software, specified by the OS running, and
 hybrid software, containing a part of the hardware to relieve the CPU load
 Software-alone:
 software RAID is the least costly and is mostly used as a native feature on
the OS.
 It is a software host-based programme that handles RAID calculations for
hard disc drives attached to it.
 It is linked and enabled when the OS loads the RAID driver through an
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8.  Hybrid:
 A hardware component is used by this software-based RAID to deliver
RAID BIOS functions from RAID BIOs on the motherboard or an HBA.
 A layer of redundant protection from a defective boot mechanism is
provided by this technology.
 The entire RAID subsystem may be affected by software-only RAID
booting from the operating system and boot errors.
 The inclusion of a hardware RAID BIOS component prevents the
subsystem from boot errors in the operating system.
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9. STANDARD LEVELS
 There were five standard levels of RAID initially, but several variants have
evolved, including many nested levels and several (mostly proprietary) non-
standard levels.
 The Storage Networking Industry Association (SNIA) standardizes RAID
levels and their related data formats in the Common RAID Disk Drive Format
(DDF) standard.
 Standard RAID levels comprise a simple collection of RAID configurations in
computer storage that use striping, mirroring, or parity techniques to construct
large, stable data stores from multiple hard drives of general purpose
computers.
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10. RAID levels contain the following features:
 It includes a collection of physical disc drives.
 The operating system considers these distinct discs in this technology as a
single logical disc.
 Data is spread through the physical drives of the array in this technology.
 Redundancy disc functionality is used to store information regarding parity.
 The parity information can be used to restore the data in case of disc failure.
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11. RAID 0 (striping)
 A striped array of discs is introduced at this stage.
 The data is broken down into blocks and the blocks are spread between discs.
 A block of data to be written / read in parallel is obtained by each disc.
 It improves the storage device's speed and efficiency.
 In Level 0, there is no parity and backup.
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12.  Advantages:
 Throughput is improved at this stage because many data requests are
probably not on the same disc.
 The disc space is completely used at this stage and provides high
performance.
 There is no overhead caused by parity controls.
 Easy to implement and a minimum of 2 drives are required.
 Disadvantages:
 It does not contain any mechanism for error detection.
 Since it is not fault-tolerance, RAID 0 is not real RAID.
 Failure of either disc results in complete loss of data in the respective array
at this time.
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13. RAID 1 (mirroring)
 Mirroring Technique is used
 RAID controller, copies the data to all the disk in the array
 provides 100% redundancy in case of a failure.
 To store the data, only half of the drive's space is used. The other half of the
drive is just a mirror for the data that is already stored.
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14.  Advantages:
 The main advantage it provides is fault tolerance.
 As compare to single drive, it offers excellent read/write speed.
 In case of disk failure, data is safe in mirror disk
 the array will function even if any one of the drives fails.
 ideal for mission critical storage, for instance for accounting systems.
 Disadvantages:
 Only half storage is used because other half storage is mirror storage
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15. RAID 2
 Consists of striping bit-level using hamming code parity for error detection.
 Each data bit in a word is registered on a separate disc at this stage, and the
ECC (error checking and correcting) code of data words is stored on various
discs.
 This degree is not commercially used because of its high cost and complex
structure.
 RAID 3 will achieve this same efficiency at a smaller cost.
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16.  Advantages:
 uses one designated drive to store parity
 uses the hamming code for error detection
 Disadvantages:
 additional drive for error detection
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17. RAID 3
 consists of byte-level striping with a dedicated parity disk
 The parity information for each disc segment is stored at this level and written
to a dedicated parity drive.
 The parity drive is accessed in the event of drive failure, and data is
reconstructed from the remaining computers.
 The missing data can be restored to the new drive until the failed drive is
replaced.
 Data can be transferred in bulk at this stage. High-speed data transfer is thus
feasible.
 The embedded ECC information is used to detect errors
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18.  Advantages:
 data is regenerated using parity drive
 high data transfer rates
 data is accessed in parallel
 Disadvantages:
 additional drive for parity
 slow performance for operating on small sized files
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20. RAID 4
 Uses block level stripping with a separate parity disk.
 It adopts a parity-based approach instead of duplicating results.
 It enables recovery of at most 1 disc failure.
 If more than one disc fails at this stage, then there is no way to recover the data
 levels 3 and 4 both require at least three discs.
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21. RAID 5 (Striping with parity)
 The most common secure RAID level
 block-level striping with DISTRIBUTED parity
 parity rotates among the drives
 It requires at least 3 drives but can work with up to 16
 RAID 5 blends RAID 0 performance with RAID 1 redundancy, but to do so
requires a lot of storage space, around one-third of the available capacity.
 Since all drives in the array simultaneously serve write requests, this level
improves write efficiency. Overall disc output, however, can suffer from write
amplification, because many steps and recalculations are needed for even
minor changes to the stripes.
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22.  RAID 5 is a good all-round device that combines storage efficiency with
outstanding safety and decent performance.
 It is suitable for servers with files and applications that have a small number of
data drives.
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23.  Advantages:
 parity is distributed across the disks in an array.
 cost effective and provides high performance.
 Transactions of reading data are very fast, whereas transactions of writing
data are much slower (due to the parity that has to be calculated).
 If a drive fails, even when the failed drive is being replaced and the storage
controller restores the data to the new drive, you will have access to all the
data.
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24.  Disadvantages:
 complex technology
 Recovery for disc failure takes longer time since parity must be determined
from all available drives.
 cannot survive in concurrent drive failure
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25. RAID 6 (Striping with double parity)
 extension of RAID 5
 contains block-level stripping with 2 parity bits
 two independent parities are generated and stored in distributed fashion among
multiple disks
 Two parities provide additional fault tolerance
 Minimum four disk are required
 higher redundancy than RAID 5 and increased read performance
 It can suffer from the same server performance overhead with intensive write
operations
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27.  Advantages:
 read data transactions are very fast.
 You will have access to all the data if two drives failure, even though the
failed drives are being replaced. RAID 6 is, therefore, more stable than
RAID 5.
 This level performs RAID 0 to strip data and RAID 1 to mirror. In this
level, stripping is performed before mirroring
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28.  Disadvantages:
 Because of the additional parity written data transactions are slower than
RAID 5.
 very limited scalability
 complex technology
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