RAID TECHNOLOGY

RAID TECHNOLOGYRedundant Array of Inexpensive DisksCONTENTSStorage devices. Optical drives. Floppy disk. Hard disk. Components of Hard disks.RAID technology.Levels in RAID technology.Summary.

Storage devices Some of the storage devices are as follows:

Optical drives such as floppy disks,CD/DVD RomHard disks.Floppy disk drives.

FLOPPY DISKCD/DVD drives

Geometry of hard diskHard disk is an organization of data on the platters.It shows where the data will be stored in each platters.They are specified by numerical values such as:Heads.Cylinders.Sectors per track.Write precompensation.Landing Zone.

Components of Hard disk.

Platters and Media

Read/Write Heads

Head Sliders, Arms and Actuator

Spindle Motor

Connectors and Jumpers

Logic Board

Integrated CacheSectors per track.

Types of Hard diskSCSI Hard disk.SATA Hard disk.IDE(ATA/PATA).IDE(Integrated Drive Electronics)IDE is older type of Hard disk . It is also called ATA/PATA hard disk.Some of the IDE hard disk are as follows:ATA-1ATAPI (ATA Packet Interface)ATA-2ATA-3: ATA/ATAPI-4ATA/ATAPI-5: Enhanced IDE (EIDEFast ATAUltra ATA

SATA(Serial ATA Hard disk)SATA is latest technology that is replaced by PATA/ATA hard disk.SATA has several advantages over PATA they are as follows:Superior cabling and connectors.Higher bandwidth.Greater reliability.

SCSI(Small Computers System Interface)These hard disks are used in workstations and servers because of following advantages:

Improved performance over IDE and SATA in multitasking and multiuser environment.

Ability to dairy chain many drivers on computer.

RAID(Redundant Array of Inexpensive Disk)RAID is the method in which information is spread across several hard disk and maximize the ability to recover information in case of hard disk crash.Some Information about RAID technology Mirroring refers to copying of data to multiple hard disks.Striping refers to splitting of data across multiple hard disks.Error correction refers to detecting hard disk failures and recovering from the failures. Error detection is done by parity checking .Different levels of RAID are as follows:RAID 0RAID 1RAID 3RAID 4RAID 5RAID 6RAID 10RAID 53

RAID 0 level

RAID 0 level specifies data stripping. It means that data will split up into several smaller parts without any parity.

It requires minimum 2 number of hard disks to operate.

RAID 0 level provides good performance over single disk storage.

RAID 1 levelSpecifies data Mirroring(same copy of data in all hard disks) but without any parity.This means data is copied to multiple disk but there is no error correction of RAID1 level like RAID 0 level also requires at least two hard disk drivers.

RAID 2 level(Stripping with parity.) RAID 2 level suggests data is split across multiple hard disk with parity bit is stored in the same hard disk . If any data is lost then we can recover disk.If any data is lost then we can recover the whole data with the help of parity bit.Minimum 2 HDD is required

RAID3 levelRAID 3 level specifies data stripping with dedicated parity disk . This means RAID 3 level generates parity and dedicated one of its hard disk drive for storing the parity information.Minimum 3 HDD is required for building RAID3 level .

RAID 3: XORExit Hamming Code, Enter XOR (eXclusive OR)

XOR in Action:01012 XOR 00112 = 01102

If ????2 XOR 11002 = 01102,Then 11002 XOR 01102 = ????2 = 10102Thus we can use XOR results to recover lost dataXOR Logic TableA XOR BResult000011101110RAID 3: Pros and ConsAdvantages:High Read/Write Transfer RatesDisk failures dont slow the systemLow Ratio of Data Disks to Parity DisksDisadvantages:Transaction rate slowed by Parity DiskComplex Controller DesignSoftware ImplementationResource Intensive

RAID 3: UsesVideo ProductionHigh-end Video and Image EditingOther uses that require high throughput of dataRAID 4 levelRAID 4 level is similar to RAID 3 except with a difference . The difference is that :In RAID 3 we stripes data one byte at time.Whereas RAID 4 strips data in blocks.

RAID 4: UsesAdvantages:Very high read ratesMultiple files read at once

Uses:Web Servers, and other high read, low write situationsDisadvantages:Very slow write ratesEven small writes fill up parity write queueInefficient data recoveryEven more Complex Controller Design than RAID 3*Has most of the other Advantages and Disadvantages of RAID 3RAID 5 levelRAID 5 took all the advantages from RAID 0-RAID 4 and build up this technology . The advantages are as follows:RAID 0-Stripping.RAID 1-Mirroring.RAID 2-Stripping bit level parity.RAID 3-Stripping with dedicated parity.RAID 4-Block level parity.Therefore , RAID 5 level has got highest popularity as it uses all the level and it is used widely.RAID 5Highest Read data transaction rate

Medium Write data transaction rate

Most complex controller design

Used For Server Applications.

RAID 10

Characterized by:- each drive duplicated- high implementation costRAID 10Uses multiple (mirrored) RAID 1 in a single arrayData striped across all mirrored setsVery high fault toleranceHigh performance rateHow are the HDD are designed in RAID technologies

Advantages of RAIDThe foremost advantage of using a RAID drive is that it increases the performance and reliability of the system. The RAID drive is a credible example that could be used in a server. The RAID increases the parity check and thus it regularly checks for any possibility of a system crash. Disk stripping is also a hot topic when we discuss about the RAID drives. The performance is much highlighting and increases a lot when the disk stripping is done. The mirroring is the complete duplication of the data. Or in the other sense the mirroring is the 100% duplication of the data on two drives. Disadvantages of RaidA major disadvantage regarding the RAID drive is that there needs to be written the drivers for a Network Operating System (NOS). Hence the major fact and also the most important usage of the RAID system is that it is essentially designed and extensively used in a server.Another disadvantage regarding the RAID is that it is very much difficult for an administrator to configure the RAID system. The ability to dynamically enlarge the RAID server is also complex process; especially for those administrators who are the IS managers and also the LAN administrators. SummaryRAIDlevel Mirroring Striping Parity Min . drives Key features 0 No Block No 2 Fastest, but lacks data protection. 1 Yes No 32No 2 Requires double capacity but fastest protectedsolution. 3 No Byte Dedicated 3 Distributes each block across disks. 4 No Block Dedicated 3 Larger blocks improve performance. Dedicated parity disk is potential bottleneck. 5 No Block Distributed 3 Eliminates parity bottleneck.Thank youANJAN KUAMR.B.-Guided by Mr. Pintunath .