Explain levels of Raid with neat diagram?

RAID Levels

➢ RAID Level selection is determined by below factors:

✓ Application performance

✓ data availability requirements

✓ cost

➢ RAID Levels are defined on the basis of:

✓ Striping

✓ Mirroring

✓ Parity techniques

➢ Some RAID levels use a single technique whereas others use a combination of techniques.

➢ Table shows the commonly used RAID levels 

1 RAID 0

➢ RAID 0 configuration uses data striping techniques, where data is striped across all the disks 

within a RAID set. Therefore it utilizes the full storage capacity of a RAID set.

➢ To read data, all the strips are put back together by the controller.

➢ Fig 1.14 shows RAID 0 in an array in which data is striped across five disks.

➢ When the number of drives in the RAID set increases, performance improves because more 

data can be read or written simultaneously.

RAID 1

➢ RAID 1 is based on the mirroring technique.

➢ In this RAID configuration, data is mirrored to provide fault tolerance (see Fig 1.15). A

➢ RAID 1 set consists of two disk drives and every write is written to both disks.

➢ The mirroring is transparent to the host.

➢ During disk failure, the impact on data recovery in RAID 1 is the least among all RAID 

implementations. This is because the RAID controller uses the mirror drive for data recovery.

➢ RAID 1 is suitable for applications that require high availability and cost is no constraint.

Nested RAID

➢ Most data centers require data redundancy and performance from their RAID arrays.

➢ RAID 1+0 and RAID 0+1 combine the performance benefits of RAID 0 with the redundancy 

benefits of RAID 1.

➢ They use striping and mirroring techniques and combine their benefits.

➢ These types of RAID require an even number of disks, the minimum being four.

RAID 3

➢ RAID 3 stripes data for high performance and uses parity for improved fault tolerance.

➢ Parity information is stored on a dedicated drive so that data can be reconstructed if a drive 

fails. For example, of five disks, four are used for data and one is used for parity.

➢ RAID 3 always reads and writes complete stripes of data across all disks, as the drives operate 

in parallel. There are no partial writes that update one out of many strips in a stripe.

➢ RAID 3 provides good bandwidth for the transfer of large volumes of data. RAID 3 is used in 

applications that involve large sequential data access, such as video streaming.

RAID 4

➢ RAID 4 stripes data for high performance and uses parity for improved fault tolerance. Data 

is striped across all disks except the parity disk in the array.

➢ Parity information is stored on a dedicated disk so that the data can be rebuilt if a drive fails. 

Striping is done at the block level.

➢ Unlike RAID 3, data disks in RAID 4 can be accessed independently so that specific data 

elements can be read or written on single disk without read or write of an entire stripe. RAID 

4 provides good read throughput and reasonable write throughput.

RAID 5

➢ RAID 5 is a versatile RAID implementation.

➢ It is similar to RAID 4 because it uses striping. The drives (strips) are also independently 

accessible.

➢ The difference between RAID 4 and RAID 5 is the parity location. In RAID 4, parity is 

written to a dedicated drive, creating a write bottleneck for the parity disk

➢ In RAID 5, parity is distributed across all disks. The distribution of parity in RAID 5 

overcomes the Write bottleneck. Below Figure illustrates the RAID 5 implementation.

➢ Fig 1.18 illustrates the RAID 5 implementation.

➢ RAID 5 is good for random, read-intensive I/O applications and preferred for messaging, data 

mining, medium-performance media serving, and relational database management system 

(RDBMS) implementations, in which database administrators (DBAs) optimize data access.

 RAID 6

➢ RAID 6 includes a second parity element to enable survival in the event of the failure of two 

disks in a RAID group. Therefore, a RAID 6 implementation requires at least four disks.

➢ RAID 6 distributes the parity across all the disks. The write penalty in RAID 6 is more than 

that in RAID 5; therefore, RAID 5 writes perform better than RAID 6. The rebuild operation 

in RAID 6 may take longer than that in RAID 5 due to the presence of two parity sets.