CompTIA A+ 220-1201 (3.4 - RAID)

Data redundancy

• 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

RAID

• 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 one parity drive

• RAID 6 - Striping with two parity drives

• Nested RAID - RAID 1+0 (a.k.a. RAID 10) - A stripe of mirrors

RAID 0 - Striping

• 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

RAID 1 - Mirroring

• 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

RAID 5 - Striping with parity

• 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

RAID 6

• Add another parity block

- Requires at least four drives

• Could lose two drives

- Data would continue to be available

• Requires another drive

- Adds more parity

- Does not add more capacity

RAID 1+0 - A stripe of mirrors

• The speed of striping, the

redundancy of mirrors

• Need at least 4 drives