3.3 - RAID

Question 1

Data redundancy

Answer 1

• Hard drives store huge amounts of important data
• Hard drives are moving components
  – They will eventually break
• What happens to the data when the drive fails?
  – You can prepare for that; Use an array of drives
• RAID is not backup

Question 2

RAID

Answer 2

• Redundant Array of Independent Disks
  – They’re also inexpensive disks.
• Different RAID levels - Some redundant, some not
• RAID 0 – Striping
• RAID 1 - Mirroring
• RAID 5 – Striping with Parity
• Nested RAID - RAID 1+0 (a.k.a. RAID 10) - A stripe of mirrors

Question 3

RAID 0 - Striping

Answer 3

• File blocks are split between
  two or more physical drives
  – High performance
  – Data written quickly
• No redundancy
  – A drive failure breaks the array
  – Raid 0 is zero redundancy

Question 4

RAID 1 - Mirroring

Answer 4

• File blocks are duplicated between
  two or more physical drives
• High disk utilization
  – Every file is duplicated
  – Required disk space is doubled
• High redundancy
  – Drive failure does not affect data availability

Question 5

RAID 5 - Striping with parity

Answer 5

• File blocks are striped
  – Along with a parity block
  – Requires at least three disks
• Efficient use of disk space
  – Files aren’t duplicated, but space
  is still used for parity
• High redundancy
  – Drive is available after a failure
  – Parity calculation may affect
  performance

Question 6

RAID 1+0 - A stripe of mirrors

Answer 6

• The speed of striping, the
  redundancy of mirrors
• Need at least 4 drives