What is RAID

1
What is RAID

• Redundant
• Array of
• Independent
• Disks

2
Lets Talk about Striping

• RAID arrays that use striping improve performance
  by splitting up files into small pieces and
  distributing them to multiple hard disks.
• File Red 140KB
• File Blue 600KB
• File Green 3.2MB
• File Purple 21.2MB

3
Two Basic Types of Striping

• Striping is available in two forms
• Single-user
• also called "large block sequential access
• Multi-user
• sometimes called "small block random access"
• Single-user striping improves performance by
  parallel data transfer
• Multi-user striping improves performance by
  overlapped seeks

4
Block Diagram of a Raid Striping Configuration
5
RAID 0 (Nonredundant)

• Striped disk array without fault tolerance.
• Best I/O performance achieved when data is
  striped across multiple controllers with only
  one drive per controller.

6
RAID 1 (Mirroring)

• For highest performance, the controller must be
  able to perform two concurrent separate reads per
  mirrored pair or duplicate writes per mirrored
  pair.

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RAID 01(Mirrored Striping)

• High data transfer performance.
• High I/O rates are achieved thanks to multiple
  stripe segments.
• Uses mirroring and striping.

8
RAID 2 (Memory-Style ECC)

• Uses Hamming Codes to detect and correct errors.
• The ECC code verifies correct data or corrects
  single disk (bit) errors.
• Extremely high data transfer rates possible.

9
Parity Bit Quiz

• 1. What is a parity bit is used for?
• single-bit error detection and correction.
• 2. What are the two types of parity bit
  calculations?
• even and odd
• 3. What is the goal of even parity?
• to have an even number of 1 bits
• 4. What is the goal of odd parity?
• to have an odd number of one bits
• 5. If the sending port reads odd parity and the
  receiving port counts seven 1s in the packet,
  the parity bit is set to what?
• a 0 bit
• 6. If the sending port reads even parity and
  the receiving port counts seven 1s in the
  packet, the parity bit is set to what?
• a 1 bit

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RAID 3 (Bit-Interleaved Parity)

• Parallel transfer with parity on the data block
  is subdivided (striped) and written the data
  disks.
• Stripe parity is generated on writes, recorded on
  the parity disk and checked on reads

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RAID 4 (Block-Interleaved Parity)

• Independent data disks with shared parity disk.
• Each entire block is written onto a data disk.
• Parity block for the same rank blocks is
  generated on writes, recorded on the parity disk
  and checked on reads.

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RAID 5 (Block-Interleaved Distributed Parity)

• Each entire data block is written on a data disk.
• Parity for blocks in the same rank is generated
  on writes, recorded in a distributed location and
  checked on reads.

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RAID 6 (PQ Redundancy)

• Independent data disks with two Independent
  parity schemes to protect against multiple disk
• Data is striped on a block level across a set of
  drives, just like RAID 5.

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RAID 7 (Proprietary)

• Optimized asynchrony for high I/0 Rates as well
  as high data transfer rates.
• Overall write performance is 25 to 90 better
  than a single spindle performance and 1.5 to 6
  times better than other array levels.
• Based on RAID 3 and 4.
• Created by Storage Computer Corporation.

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RAID 10 (Striped Mirroring)

• Also known as RAID 10 and 1/0
• Very high reliability combined with high
  performance.
• High I/O rates are achieved by striping RAID 1
  segments.

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RAID 53 (Striped Array of Arrays)

• High I/O rates and data transfer performance
• High data transfer rates are achieved thanks to
  its RAID 3 array segments.
• High I/O rates for small request are achieved
  thanks to its RAID 0 striping.