1 / 31

Data Protection: RAID

Data Protection: RAID. Chapter 3. Presented by: Anupam Mittal. Lecture 7. Data protection: Concept of RAID and its Components. Chapter Objectives. After completing this chapter, you will be able to: Describe what is RAID and the needs it addresses

summer
Download Presentation

Data Protection: RAID

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Data Protection: RAID Chapter 3 Presented by: Anupam Mittal

  2. Lecture 7 • Data protection: Concept of RAID and its Components Data Protection: RAID

  3. Chapter Objectives After completing this chapter, you will be able to: • Describe what is RAID and the needs it addresses • Describe the concepts upon which RAID is built • Define and compare RAID levels • Recommend the use of the common RAID levels based on performance and availability considerations • Explain factors impacting disk drive performance Data Protection: RAID

  4. Why RAID • Performance limitation of a single drive disk drive • Limited Capacity • Limited access speed • An individual drive has a certain life expectancy • Measured in MTBF • Example - If the MTBF of a drive is 750,000 hours, and there are 100 drives in the array, then the MTBF of the array becomes 750,000 / 100, or 7,500 hours • RAID was introduced to mitigate this problem • RAID provides: • Increase capacity • Higher availability • Increased performance Data Protection: RAID

  5. RAID - Redundant Array of Independent Disks RAIDController Host RAID Array RAID Arrays

  6. Host RAID Array Components Physical Array Logical Array RAIDController Hard Disks RAID Array Data Protection: RAID

  7. RAID Implementations • Hardware (usually a specialized disk controller card) • Controls all drives attached to it • Array(s) appear to host operating system as a regular disk drive • Provided with administrative software • Software • Runs as part of the operating system • Performance is dependent on CPU workload • Does not support all RAID levels Data Protection: RAID

  8. RAID Levels • 0 Striped array with no fault tolerance • 1 Disk mirroring • 3 Parallel access array with dedicated parity disk • 4 Striped array with independent disks and a dedicated parity disk • 5 Striped array with independent disks and distributed parity • 6 Striped array with independent disks and dual distributed parity • Nested RAID (i.e., 1 + 0, 0 + 1, etc.) Data Protection: RAID

  9. 0 4 8 RAID Redundancy: Parity 1 5 9 2 RAIDController 6 10 3 7 Host 11 0 1 2 3 4 5 6 7 8 9 10 11 Parity Disk RAID Arrays

  10. The middle drive fails: Parity Calculation Data 5 5 + 3 + 4 + 2 = 14 Data 3 Data 4 5 + 3 + ? + 2 = 14 ? = 14 – 5 – 3 – 2 ? = 4 Data 2 Parity 14 RAID Array RAID Arrays

  11. Lecture 8, 9, 10 • Different RAID levels and their suitability for different application environments: RAID 0, RAID 1 RAID Arrays

  12. Strips Stripe Stripes Data Organization: Striping Stripe 1 Strip 2 Strip 3 Strip 1 Strip 1 Strip 2 Strip 3 Stripe 1 Stripe 2 Data Protection: RAID Strips

  13. RAIDController Host RAID 0 – Striped Array with no Fault Tolerance 0 1 5 9 2 6 10 3 7 11 Data Protection: RAID

  14. Block 1 Block 0 Block 1 Block 1 Block 0 Block 0 RAID 1 – Disk Mirroring RAIDController Host Data Protection: RAID

  15. RAID 1 RAIDController RAID 0 Host Block 3 Block 2 Block 1 Block 0 Block 3 Block 2 Block 1 Block 0 Nested RAID – 0+1 (Striping and Mirroring) Data Protection: RAID

  16. RAID 1 RAIDController RAID 0 Host Block 3 Block 1 Block 2 Block 3 Block 0 Block 1 Block 3 Block 0 Block 0 Block 1 Block 2 Block 2 Nested RAID – 0+1 (Striping and Mirroring) Data Protection: RAID

  17. RAID 0 RAIDController RAID 1 Host Block 3 Block 3 Block 1 Block 0 Block 0 Block 1 Block 2 Block 2 Nested RAID – 1+0 (Mirroring and Striping) Data Protection: RAID

  18. RAID 0 RAIDController RAID 1 Host Block 0 Block 0 Block 2 Block 2 Block 3 Block 3 Block 1 Block 1 Block 0 Block 2 Nested RAID – 1+0 (Mirroring and Striping) Data Protection: RAID

  19. RAID 0+1 vs. RAID 1+0 • Benefits are identical under normal operations • Rebuild operations are very different • RAID 1+0 uses a mirrored pair – only 1 disk is rebuilt if a disk fails • RAID 0+1 if a single drive fails, the entire stripe is faulted • RAID is 0+1 is a poorer solution and is less common RAID Arrays

  20. 0 4 8 RAID Redundancy: Parity 1 5 9 2 RAIDController 6 10 3 7 Host 11 0 1 2 3 4 5 6 7 8 9 10 11 RAID Arrays Parity Disk

  21. RAIDController Host The middle drive fails: RAID Redundancy: Parity 0 4 1 6 5 9 1 ? 3 7 7 11 Parity calculation 4 + 6 + 1 + 7 = 18 0 1 2 3 4 5 6 7 18 4 + 6 + ? + 7 = 18 ? = 18 – 4 – 6 – 7 ? = 1 Data Protection: RAID Parity Disk

  22. RAIDController ParityGenerated Host Block 1 Block 2 Block 3 Block 0 Block 3 Block 2 Block 1 Block 0 P 0 1 2 3 RAID 3 – Parallel Transfer with Dedicated Parity Disk Data Protection: RAID

  23. P 0 1 2 3 P 0 1 2 3 Block 1 Block 3 Block 2 Block 0 Block 0 P 4 5 6 7 Block 5 Block 7 Block 6 Block 4 RAIDController Block 0 Block 0 ParityGenerated P 0 1 2 3 RAID 4 – Striping with Dedicated Parity Disk Host RAID Arrays

  24. P 0 1 2 3 P 0 1 2 3 Block 0 Block 0 Block 3 Block 1 Block 2 ParityGenerated P 4 5 6 7 P 4 5 6 7 Block 5 Block 6 Block 4 Block 4 Block 7 RAIDController Block 0 Block 4 Block 0 Block 4 P 4 5 6 7 ParityGenerated Host P 0 1 2 3 RAID 5 – Independent Disks with Distributed Parity Data Protection: RAID

  25. RAID 6 – Dual Parity RAID • Two disk failures in a RAID set leads to data unavailability and data loss in single-parity schemes, such as RAID-3, 4, and 5 • Increasing number of drives in an array and increasing drive capacity leads to a higher probability of two disks failing in a RAID set • RAID-6 protects against two disk failures by maintaining two parities • Horizontal parity which is the same as RAID-5 parity • Diagonal parity is calculated by taking diagonal sets of data blocks from the RAID set members • Even-Odd, and Reed-Solomon are two commonly used algorithms for calculating parity in RAID-6 Data Protection: RAID

  26. RAID Implementations • Hardware (usually a specialized disk controller card) • Controls all drives attached to it • Performs all RAID-related functions, including volume management • Array(s) appear to the host operating system as a regular disk drive • Dedicated cache to improve performance • Generally provides some type of administrative software • Software • Generally runs as part of the operating system • Volume management performed by the server • Provides more flexibility for hardware, which can reduce the cost • Performance is dependent on CPU load • Has limited functionality RAID Arrays

  27. Lecture 11 • Comparison of RAID Levels Data Protection: RAID

  28. RAID Comparison Data Protection: RAID

  29. D4 D2 D1 P0 D3 RAID Impacts on Performance RAID Controller • Small (less than element size) write on RAID 3 & 5 • Ep = E1 + E2 + E3 + E4 (XOR operations) • If parity is valid, then: Ep new = Ep old – E4 old + E4 new (XOR operations) • 2 disk reads and 2 disk writes • Parity Vs Mirroring • Reading, calculating and writing parity segment introduces penalty to every write operation • Parity RAID penalty manifests due to slower cache flushes • Increased load in writes can cause contention and can cause slower read response times Ep new Ep old E4 old E4 new = - + 2 XOR Ep new Ep old E4 old E4 new Data Protection: RAID

  30. RAIDController Hot Spares Data Protection: RAID

  31. Check Your Knowledge  • What is a RAID array? • What benefits do RAID arrays provide? • What methods can be used to provide higher data availability in a RAID array? • What is the primary difference between RAID 3 and RAID 5? • What is advantage of using RAID 6? • What is a hot spare? Data Protection: RAID

More Related