1. CHAPTER Network Reliability: Fault Tolerance and Other Issues

2. Chapter Objectives Discuss network reliability issues –Fault tolerance, tape backup, UPS etc Describe different levels of fault tolerance –Levels 1, 2 and 3 –Examine the relevance of file allocation tables to fault tolerance Explain RAID technology

3. Chapter Modules An overview of network reliability Level 1 fault tolerance Level 2 and level 3 of fault tolerance Practical implementation examples RAID

4. END OF CHAPTER INTRODUCTION

5. MODULE An Overview of Network Reliability

6. Importance of Fault Tolerance Mission critical applications are today run on networks in many organizations Important to provide built-in fault tolerance in networks to support mission critical applications

7. Fault Tolerance The ability to continue to function when a fault occurs Example – A server with built-in fault tolerance can continue to operate even when one of its hard disks fails

8. Focus of Fault Tolerant Features Most fault tolerance features are centered on a server –Disk storage in the server is the focal point of a number of fault tolerant features –Mechanical components are more susceptible to failure than electronic components –The hard disk is most vulnerable to failure in a server A number of fault tolerant features address the possible failure of hard disks

9. Fault Tolerance Implementation Software based Hardware based A combination of both

10. Sever Based Implementation of Fault Tolerance Level 1 Level 2 Level 3

11. Preview of Fault Tolerance Based on the premise of maintaining multiple copies of critical components Level 1 –Duplicate FATs Level 2 –Duplicate server hard disks Level 3 –Duplicate servers

12. RAID Storage: The Practical Implementation Redundant Array of Independent Disks Data is stored in a RAID subsystems A largely hardware-based implementation

13. Other Features Uninterruptible Power Supply (UPS) Tape backup

14. Uninterruptible Power Supply (UPS) Ensures the uninterruptible supply of power to the server Batteries in the UPS will continue to provide power in the event of a power outage

15. UPS Implementations AS-400 example –When the power goes down the UPS takes over and systematically shuts down the system preserving the data files Other implementations –Power loss----  UPS takes over -  –-  Standby generator is activated by sensors –The process is reversed when the power come back

16. Tape Backup Used more as a precautionary measure than a fault tolerant measure Data on the server is periodically backed up on a tape If the disk storage fails on the server: –A previously stored version of the data is loaded on to a newly installed disk storage on the server Offers some degree of protection against the total loss of data

17. Network Operating System Support for Reliability Support for Levels 1 and 2 of fault tolerance is readily available in network operating systems Currently support is also available for Level 3 fault tolerance as well RAID 0,1 and 5 are commonly supported

18. END OF MODULE

19. MODULE Level 1 Fault Tolerance

20. A Software Based Solution

21. Support for Fault Tolerance Provided by the network OS Support for Level 1 and 2 has been available in OS for a period of time Newer operating systems have support for Level 3 fault tolerance –Support for RAID is also incorporated RAID may be considered as an extension of Level 2 fault tolerance

22. Level 1 Fault Tolerance A backup copy of the File Allocation Table (FAT) is kept on the server disk NOS uses the backup FAT should the original FAT become corrupted –This would ensure the continued operation of the server The problem should be rectified as soon as possible

23. File Allocation Table (FAT) File A Size 34K ---- Start Sector 1 Track 2 FATBackup FAT FAT

24. A Summary of File Allocation Table (FAT) Features Keeps track of files on the disk Uses pointers to point to the location of the files –Tracks, sectors Stores file related information –Size, date last modified, security information etc. If a FAT is corrupted, none of the files on the disk can be retrieved

25. A Note on File Systems Newer file systems have been introduce following FAT16 FAT32 –Windows 95/98/ME systems –Windows 2000 OS NTFS –Windows NT related filing technology –Windows 2000 HPFS –OS/2 related filing technology Linux –ext2

26. Newer File System Characteristics Support longer file names Better security Support larger hard disks Abide by Uniform Naming Convention (UNC) Provide by Better security –Allows greater control to be exercised on the access to directories, files etc.

27. Format of Uniform Naming Convention \\computer_name\directory_name\file_na me

28. END OF MODULE

29. MODULE Levels 2 and 3 of Fault Tolerance

30. Levels 2 and 3 A dominantly hardware based solution Obviously, software support in the OS also required

31. Level 2 Fault Tolerance (FT) Implemented by installing a duplicate disk in the server The server data is duplicated on the second disk in real-time to provide fault tolerance The duplication process itself is automatic when a NOS that supports Level 2 FT is used In the event of a failure of the primary hard disk, the network will continue to operate using the secondary hard disk –However, immediate action must be taken to replace the failed hard disk

32. Level 2 FT Implementation Types of Implementation –Disk Mirroring –Disk Duplexing Disk Mirroring –One controller supporting two drives Disk Duplexing –Two controllers and two drives –Each drive would have its own controller –Better protection compared to disk mirroring

33. Level 2 Fault Tolerance Implementation HD Controller HD Controller HD Controller DuplexingMirroring

34. Level 3 Fault Tolerance Dual interconnected servers are used to support the network –Second server is simply a mirror of the first server Data mirroring is done automatically by the NOS that supports Level 3 fault tolerance

35. Level 3 Fault Tolerance Implementation Main Server Mirrored Server Work Stations High-Speed Link

36. Actual Implementation of Fault Tolerance Level 1 is universally deployed Level 2 requires additional hardware –Best deployed by using the RAID storage subsystem Level 3 requires considerably more hardware and software resources –Largely used in networks that support mission critical applications

37. END OF MODULE

38. MODULE RAID Storage Subsystem

39. RAID Storage Redundant Array of Independent Disks Data is stored striped over different disk in a RAID storage subsystem

40. Purpose of RAID Provide fault tolerance Offer better performance

41. RAID Basics Data is stored striped over multiple disks –Data striping is the fundamental concept pursued by RAID Data can be recreated from the redundant disks MTBF (Mean Time Between Failure) is reduced (MTBF of a disk/number of disks in the subsystem???)

42. RAID Storage Standards RAID 0 through RAID 5 Popular RAID formats –RAID 0, RAID 1, RAID 5 Other formats –RAID 10 and RAID 50

43. RAID 0 Data is simply stored striped over multiple disks Does not offer fault tolerance Offers better performance –Multiple heads access the data stored on the different drives for faster data access

44. RAID 0 Striping Source: Adaptech

45. More on Striping Striping logically divides each hard disk into stripes The stripes are arranged interleaved in a rotating sequence among the various disks Data stored in the stripes for a logical sequence of storage space composed alternatively of stripes from each disk (drive) A stripe can be as small as a sector (512 bytes) or as large as several megabytes –In general, a record falls entirely within one stripe

46. RAID 0 Data Access Performance Source: Adaptech

47. Multiple I/O Access Most operating systems support concurrent disk I/O I/O load must be balanced on the disks for optimum performance Striping promotes load balancing and hence improves disk I/O performance

48. RAID 0 Configuration Large stripes for multiple users Small stripes for single users

49. Advantages and Disadvantages Fast access If one disk fails, the entire system will no more be able to use the data on all the disks

50. Windows Support for RAID 0 Windows 2003 supports RAID 0 2 to 32 disks can be used in a set known as a striped volume

51. RAID 1 Provides fault tolerance Basically implements disk mirroring

52. Implementation A single pair of mirrored disks are not striped Multiple pair of mirrored disks can be striped to create striped volumes

53. RAID 1 in Operation Source: Adaptec

54. RAID 1 Performance Read performance is improved because both disks can be simultaneously read for different records Write performance remains unchanged as the same data need to be written to both disks

55. Windows Support for RAID 1 Supported in Windows 2000 –Ftdisk.sys is the driver use for supporting fault tolerance

56. RAID 5 Provides fault tolerance using Parity Data and parity information is distributed over all the disks

57. Read and Write Operation with RAID 5 Source: Adaptech

58. Read and Write Performance Read access can be overlapped –Because data is spread over different drives Write operations could also be overlapped –Because different data records store the parity information in different disks

59. Windows Support Supported in Windows 2000 Known as “stripe set with parity on basic disks” Requires at least 3 disks An additional 16 Mbytes of memory must be provided to support RAID 5

60. RAID 10 Offers the advantage of both RAID 0 and RAID 1 –Faster performance through multiple read access –Fault tolerance through disk mirroring Also known as RAID 0+1

61. RAID 50 Combines the advantages of RAID 0 and RAID 5

62. Summary (Source: Adaptec) RAID 0 offers good read and write performance, but it does not provide fault tolerance RAID 1 offers fault tolerance, but it does not in general offer performance advantage –Multiple pairs may be created for performance advantage in addition to providing fault tolerance

63. Summary (Continued) RAID 5 combines efficient, fault-tolerant data storage with good performance characteristics. However, write performance and performance during drive failure is slower than with RAID 1. Rebuild operations also require more time than with RAID 1 because parity information is also reconstructed. At least three drives are required for RAID 5 arrays.

64. END OF MODULE

65. MODULE An Assembly of Fault Tolerance and Backup Features

66. Fault Tolerant Components RAID storage subsystem Redundant power supplies Uninterruptible Power Supply or UPS Tape backup device

67. Hardware Systems for Reliability Server Client RAID Tape UPS Redundant Power Supply With Surge Protector

68. UPS

69. Tape Backup Technology QIC Travan DAT 8mm Mammoth AIT technology Digital Linear Tape Super DLT ADR technology Linear Tape Open VXA technology Robotic applications http://www.pctechguide.com/15tape2.htm

70. Web Research Obtain information on RAID 0, 1, 5 and 10 –Adaptec –http://www.acnc.com/04_01_00.html#tophttp://www.acnc.com/04_01_00.html#top –Get the information on different file systems including the Linux and Unix file systems Visit the website of an UPS vendor to get additional information on UPC –APC –PC Power and Cooling Tape backup –http://www.pctechguide.com/15tape.htm#QIC

71. Firewall and Protocols

72. Software Firewall Settings ICMP etc. Check Zone Alarm Pro

73. END OF MODULE END OF CHAPTER