1 Advanced Database Systems Dr. Fatemeh Ahmadi-Abkenari September 2013

2 RAID Systems edundant rray of Independent/ Inexpensive isks Redundant Array of Independent/ Inexpensive Disks A lower level approach to the performance bottleneck caused by disk I/O Characteristics:  Increasing the availability of data in crash time  Better throughput than a single disk  Concurrent handling of multiple request  Improving the request involving large block of data  Transfer time reduction

3 RAID Systems Terminology:  Mirroring  Striping  Chunks 3- The unit of data to be spread 2- Spread of data across an array of disks 1- One type of redundant storage RAID LEVELS:  BASIC LEVELS (0, 1, 3, 5)  HYBRID LEVELS (01, 10, 03, 30, 50, 100, …)

4 RAID Levels Level 0 Level 0:  Uses only Striping and no Redundancy  A failure of a single disk is devastating

5 RAID Levels Level 1 Level 1:  Uses no Striping and only Mirroring  High durability  Expensive for many applications

6 RAID Levels Level 3 Level 3:  Uses Striping and a type of Redundancy  Chunks are at byte level  The (n+1) st disk is the Parity disk  Parity disk stores the XOR of the corresponding bytes on the other n disks  High transfer rate  Useful for application with real-time requirement

abc = a XOR b bca abcd = a XOR b XOR c RAID Levels Level 3

A1: A2: A3: Ap (1-3): RAID Levels Level 3

9 RAID Systems Level 5 Level 5:  Uses Striping and Redundancy  Stores Parity information  No single parity disk

10 Hybrid RAID Systems Level 10 Level 10: Combination of Level 0 and Level 1

11 Hybrid RAID Systems Level 01

12 Hybrid RAID Systems Level 30

13 Hybrid RAID Systems Level 03

14 Hybrid RAID Systems Level 50

15 Level 100 Hybrid RAID Systems

16 Cylinder Track Spindle Platter Sector Arm Assembly Read/Write Head Disk Organization

A: Track B: Mathematical Sector C: Disk Sector (Data Unit) D: Cluster

18 Disk Organization

19 Disk Organization Terminology:  Page: The unit of data transferred with each I/O operation  Block: is a sequence of adjacent sectors on a track  Cache: An array of page-size buffers in main memory  Hit: If an application refer to an item in a page exists in cache Trade-off Choosing the number of sectors in a block (page size)

For Further Reading; Database Systems, An application-Oriented Approach Second Edition Chapter 9 Michael Kifer, Arthur Bernstein, Philip M. Lewis Pearson, Addison Wesley Publication 2006