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Redundant Array of Inexpensive Disks

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CONTENTS Storage devices. Optical drives. Floppy disk. Hard disk. Components of Hard disks. RAID technology. Levels in RAID technology. Summary.

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Storage devices Some of the storage devices are as follows: Optical drives such as floppy disks,CD/DVD Rom Hard disks.

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Floppy disk drives. FLOPPY DISK

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CD/DVD drives

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Geometry of hard disk Hard 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.

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Components of Hard disk. o Platters and Media o Read/Write Heads o Head Sliders, Arms and Actuator o Spindle Motor o Connectors and Jumpers o Logic Board o Integrated Cache

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Sectors per track.

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Types of Hard disk SCSI Hard disk. SATA Hard disk. IDE(ATA/PATA).

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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-1 ATAPI (ATA Packet Interface) ATA-2 ATA-3: ATA/ATAPI-4 ATA/ATAPI-5: Enhanced IDE (EIDE Fast ATA Ultra ATA

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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.

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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.

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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.

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Some Information about RAID technology i. Mirroring refers to copying of data to multiple hard disks. ii. Striping refers to splitting of data across multiple hard disks. iii. Error correction refers to detecting hard disk failures and recovering from the failures. Error detection is done by parity checking.

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Different levels of RAID are as follows: RAID 0 RAID 1 RAID 3 RAID 4 RAID 5 RAID 6 RAID 10 RAID 53

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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.

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RAID 1 level Specifies 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.

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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

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RAID3 level RAID 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.

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RAID 3: XOR Exit Hamming Code, Enter XOR (eXclusive OR) XOR in Action: 0101 2 XOR 0011 2 = 0110 2 If ???? 2 XOR 1100 2 = 0110 2, Then 1100 2 XOR 0110 2 = ???? 2 = 1010 2 Thus we can use XOR results to recover lost data XOR Logic Table A XOR BR esult 000 011 101 110

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RAID 3: Pros and Cons Advantages: High Read/Write Transfer Rates Disk failures dont slow the system Low Ratio of Data Disks to Parity Disks Disadvantages: Transaction rate slowed by Parity Disk Complex Controller Design Software Implementation Resource Intensive

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RAID 3: Uses Video Production High-end Video and Image Editing Other uses that require high throughput of data

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RAID 4 level RAID 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.

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RAID 4: Uses Advantages: Very high read rates Multiple files read at once Uses: Web Servers, and other high read, low write situations Disadvantages: Very slow write rates Even small writes fill up parity write queue Inefficient data recovery Even more Complex Controller Design than RAID 3 *Has most of the other Advantages and Disadvantages of RAID 3

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RAID 5 level RAID 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.

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RAID 5 Highest Read data transaction rate Medium Write data transaction rate Most complex controller design Used For Server Applications.

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RAID 10 Characterized by: - each drive duplicated - high implementation cost

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RAID 10 Uses multiple (mirrored) RAID 1 in a single array Data striped across all mirrored sets Very high fault tolerance High performance rate

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How are the HDD are designed in RAID technologies

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Advantages of RAID The 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.

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Disadvantages of Raid A 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.

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Summary RAID level 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 protected solution. 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.

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Thank you ANJAN KUAMR.B. -Guided by Mr. Pintunath.