Question

Computer Architecture

Theme: External Memory

Very briefly define the seven RAID levels, providing information about stripe size, synchronization, data transfer rate and their applications. (total less than a page)

Answer 1

External memory

External memory is an storage of an external hard drive or internet. The different types of external memories are :

• CD
• DVD
• Memory card
• Flash drive
• Cloud storage
• External hard drives
• PC card

The secondary memory is also called external memory. The various storage media in which a computer can store datas and programs. The secondary storage can be removable or fixed.

The seven RAID levels

RAID : Redundant Array of Independent Disk

The most common RAID levels are 0,1,5,6. RAID is a form of redundancy used to deal with hard disk failure. RAID is a set of physical drives viewed by the operating system as a single logical drive. Redundant disk capacity is used to store parity information.

The seven RAID levels are:

• RAID 0
• RAID 1
• RAID 2
• RAID 3
• RAID 4
• RAID 5
• RAID 6

RAID 0

• It has no redundancy.
• Disk array provides high input or output execution rates.
• A single input or output request consist of multiple logically configuous strips.
• The logical disk is divided into strips. It may be physical blocks or sectors.

RAID 1

• It is very simple and also known as disk mirror.
• Redundancy is acieved by duplicating all the data.
• Read request can be serviced by the lowest access time disk.
• Write request can be updating in parallel both strips.
• when a drive is fails, the data may sill be accessed from the second drive.

RAID 2

• It uses a dedicated humming code parity for stripping occurs the bit level..
• All member disk participate in the execution of every input or output requests.
• The individual drives are synchronized. Each disk head in the same position on each disk at any given time.

RAID 3

• It uses stripping and dedicates one drive to storing parity information.
• Data recovery is calculating the exclucive information recorded on the other drives.
• It cannot overlap input or output. So RAID 3 is the best for single user systems with long record applications.
• The parity bit is computed for the set of individual bits in the same position on the all data disks.   

RAID 4

• It uses large strips for user can read records from any single drive.
• More suitable for applications that have high input or output request rates.
• Less suitable for applications that require high transfer rates.
• Bit by bit parity calculated accross corresponding strips on each disks.

RAID 5

• It is a parity block level stripping.
• Distribution of parity accross all drives avoids potential input or output bottle neck.
• Concurrent access to the partial bits are multiplexed.
• When a disk fails, It take a long time to rebuild a RAID 5 array.

RAID 6

• It is similar to RAID 5.
• It includes a second parity scheme distributed across the drives in the array.
• The array have slower write performance than RAID 5 array.
• Two different parity calculations are carried out and stored in separate blocks on different disk.

Providing information about stripe size

Stripping is used across disk drives in RAID storage, network interface controllers, Disk arrays. The RAID 0 is fails for a single member drive of the RAID array causes all stored data to be lost. RAID 5 contains distributed parity and provides redundancy.

RAID synchronization is preventative maintainence porcedure to reduce the risk of an array rebuild failure.

Data Transfer Rate

Data transfer rate is used to measure how fast data is transfered from one location to another. Data transfer rate is measured in bit per second (bps).

All websites , online and offline applications use RAID to improve performance, and prevent data lose.

Recommended Applications

RAID 0

• Image editing
• Vedio production and editing
• Any applications requies high band width
• Pre press applications.

RAID 1

• Financial
• Payroll
• Accounting

RAID 3

• Vedio editing
• Image editing
• vedio production and live streaming
• Pre press applications

RAID 5

• Interanet servers
• Database servers
• File and application servers
• News servers
• WWW
• Emails