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RAID Arrays
Jul 12, 2024
Lecture on RAID Arrays
Introduction
RAID
: Redundant Array of Independent (previously Inexpensive) Disks.
Purpose: Maintain uptime and availability if a drive fails.
Important
: RAID is not a backup method, but a redundancy option.
Types of RAID
RAID 0 (Striping)
Configuration
: At least 2 drives.
Data Distribution
: Splits data evenly across drives.
Example: File with 8 blocks
Block 1 on Disk 0, Block 2 on Disk 1, Block 3 on Disk 0, etc.
Advantage
: Performance increase (only half data to read/write if 2 drives).
Disadvantage
: Zero redundancy—losing one drive means losing all data.
Remember
: RAID 0 = 0 redundancy.
RAID 1 (Mirroring)
Configuration
: At least 2 drives.
Data Distribution
: Duplicates data across both drives.
Advantage
: Full redundancy—losing one drive means data is still accessible from the other drive.
Disadvantage
: Requires twice the storage space (duplicate data on both drives).
Scenarios
: Drive loss may go unnoticed until alert is received.
RAID 5 (Striping with Parity)
Configuration
: Minimum 3 drives.
Data Distribution
: Stripes data similar to RAID 0.
Advantage
: Efficient use of drive space with added parity for redundancy.
Example
: 4 drives in RAID 5
3 drives for data, 1 for parity.
Parity is distributed across drives.
Recovery
: Parity allows data to be rebuilt if a drive is lost.
Performance may take a hit during real-time data rebuilding, depends on RAID controller/CPU.
RAID 10 (RAID 1+0 / Stripe of Mirrors)
Configuration
: Combination of RAID 0 and RAID 1.
Example: RAID 0 with 3 drives, each mirrored (RAID 1).
Data Distribution
: Even distribution and mirroring of stripes.
Advantage
: High redundancy—data remains accessible even if several drives are lost, as long as they're from different mirrored pairs.
Example: Can lose up to 3 drives in a mirrored array and still have data access.
Conclusion
Selecting the right RAID level is crucial for maintaining data availability and system performance.
Consider trade-offs: storage efficiency, redundancy, and performance.
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