Lecture Notes: RAID Arrays and Data Redundancy

Introduction to Hard Drives and Data Storage

• Hard drives are commonly used for storing large amounts of information.
• Data can be stored in terabytes on a single spinning drive.
• Hard drives have moving parts and will eventually fail.

Importance of Data Redundancy

• Data redundancy ensures data is available even when a drive fails.
• RAID arrays are configured to provide data redundancy.
• RAID is not a backup method, but a way to maintain uptime and availability.

Understanding RAID

• RAID: Redundant Array of Independent Disks (previously Inexpensive Disks)
• Uses multiple storage drives to work together for uptime and availability.
• Different RAID levels provide different features and capabilities.

Overview of RAID Levels

RAID 0: Striping

• Requires at least two drives.
• Data is split evenly between drives (e.g., a file with 8 blocks: blocks alternate between Disk 0 and Disk 1).
• Increases performance by reading/writing half the data across drives.
• Con: Zero redundancy; data loss if any drive fails.

RAID 1: Mirroring

• Data is duplicated across both drives.
• Each drive is a mirror image of the other.
• Requires twice the storage space compared to RAID 0.
• Pro: Data remains available if one drive fails.
• Con: Less efficient use of storage.

RAID 5: Striping with Parity

• Data is spread across drives with additional parity information on one drive.
• More efficient than RAID 1 for storage.
• Parity allows rebuilding of data if any drive fails.
• Con: Performance hit during real-time data recalculation using parity.

RAID 10: RAID 1 + 0 (Stripe of Mirrors)

• Combines RAID 0 and RAID 1 benefits.
• Distributes files across multiple drives and mirrors them.
• Can lose multiple drives and still retain data, provided they are part of different RAID 1 mirrors.

Conclusion

• Proper RAID configuration is crucial to ensure data redundancy and availability.
• Select the appropriate RAID level based on needs for performance, redundancy, and storage efficiency.