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GSW MCSE Notes Home Networking Essentials Notes NT Server 4.0 Notes NT Administration Notes

Module 7: Managing Fault Tolerance

Fault tolerance is the  the ability of a computer or OS to respond to a catastrophic event, such as power outage or a hardware failure, so that no data is lost, and that work in progress is not corrupted.

RAID provides fault tolerance by implementing data redundancy. There are 5 levels:

RAID 0 Volume sets & Disk striping without parity (just for study)
  • NO FAULT TOLERANCE
  • Both are "Lose one, lose 'em all.
RAID 1 Disk mirroring / duplexing.
RAID 2 Disk striping with Error-Correction-Code (ECC).
RAID 3 Disk striping with ECC stored as parity.
RAID 4 Disk striping large blocks; parity stored on one drive.
RAID 5 Disk striping with parity distributed on multiple drives.

Only RAID 0, RAID 1 and RAID 5 are supported be Windows NT Server, not Windows NT Workstation.

RAID 1: Mirror Set and Disk Duplexing

Mirror Sets

 Disk Duplexing

RAID 5: Stripe Sets with Parity

Breaking a Mirrored Set

When a member of a mirrored set fails, the functional member will continue to operate. To replace the failed disk the administrator must first break the mirror set by doing the following:

  1. In Disk Administrator use the Break Mirror on the Fault Tolerance menu. Automatically the mirrored (secondary) volume is assigned the next available drive letter. This is the first step!
  2. If the failed drive is the primary member of the set, it may be necessary to assign the drive letter that was previously assigned to the complete set. Think what happens to the shares on the set if you don't!
  3. Delete the failed partition.
  4. Use free space on another disk to create a new mirror set relationship.
  5. The computer must be restarted!

 

Fault Tolerance Specifications

RAID 0 -means- NOT fault tolerant. Windows NT SERVER only supports RAID 0, 1 and 5. NT Workstation natively supports RAID 0 AKA, it does not have fault tolerance -- built in anyway.

RAID Level 2 - Disk Striping with error correction code (ECC)
RAID Level 3 - Disk Striping with ECC stored as parity
RAID Level 4 - Disk Striping large blocks; parity stored on one drive
 

RAID Summary Chart

  Volume Set Mirror Duplex Disk Striping without Parity Disk Striping with parity
RAID 0 1 1 0 5
# Disks required 1 (2- 32 areas per volume) 2 same controller 2 not same controller 2 3
Max # disks 32 areas per vol.     32 32
Contain system / boot partition No Yes Yes No No
Can be extended without data loss Yes     No  
Can be decreased without data loss No     No  
File Systems Must be the same on all volumes     and/or: 
FAT, NTFS ; can put multiple file systems together
NTFS only
Different Types of Hard Disks together       Yes  
Advantage disk space ; best method w/out fault tolerance  potential read performance gain reduce bus traffic and potential read performance gain; also protect against controller failure I/O speed gain. Fastest read/write performance of all disk sets I/O speed gain. 2nd Fastest read/write performance of all disk sets 
Disadvantage no fault ; no performance gain write 
performance ; cost
cost no fault ; space requires 3x more memory for parity calcs.- AKA - memory hog and space hog!
Supports Removable media? Can be done but not recommended unless you plan to use removable media as fixed disk.  Can be done but not recommended unless you plan to use removable media as fixed disk.   No  
Paging File Can be placed but no performance gains Can be placed but no performance gains Can be placed but no performance gains Can be placed but no performance gains Should not be implemented on ; causes poor performance
"Lose one you lose em all" Yup     Yup  

 

Creating RAID 0, RAID 1, and RAID 5 Disks

Creating a Volume Set

Extending a Volume Set when a Volume Set is already created

Creating a Stripe Set without Parity

Creating a Disk Mirror / Duplex

Creating a Stripe Set with Parity

RAID 1 Failure: Disk Mirrors And Duplex Failure

Disk Alarm!Note: It looks easy enough, but recovery in RL (real life) is a whole different story. Disaster recovery is a very, very complex undertaking and demands careful planning and testing both at the hardware and software level -- do it -- before you actually have to!

Overview

Fixing Broken Mirrors And Duplexes

RAID 5 Failure: Stripe Set with Parity

Overview

Fixing Failed Members of a Stripe Set

Windows NT Boot Disk - this is not the same disk as the Emergency Repair Disk

Windows NT Boot Disk Fixes - NT boot disk can access a drive that has NTFS or FAT file system installed. Boot disk useful for:

Note

To create a fault tolerance boot disk:

Intel x86-based computers  RISC-based computers
Ntldr Osloader.exe
NTdetect.com Hal.dll
NTbootdd.sys (for small computer system interface (SCSI) disks not using a SCSI BIOS)* *.pal (Alpha only)
Boot.ini

*The NTbootdd.sys file appears only on SCSI systems in which the SCSI BIOS is not used!

Variable  Value
Osloader Multi(0)disk(0)fdisk(0)\Osloader.exe
Systempartition Multi(0)disk(0)fdisk(0)
Osloadpartition Path to the secondary mirrored partition.
osloadfilename Path to the Windows NT Server root directory.

Multi(0)disk(0)rdisk(1)partition(2)

Convention  Description
Multi | scsi Identifies the controller type. It can either be SCSI or some other type (multi).
(x) Identifies the hardware adapter

(starts with 0).

Disk (y) SCSI bus number.

For multi the value is always 0. 

Rdisk(z) Disk number (ignored for SCSI controllers).

(start with 0)

Partition(a) Partition number

(start with 1)

this one is the odd ball; all the rest start with 0

 The SCSI ARC naming convention varies the disk() parameter for successive disks on one controller; the multi controller format varies the rdisk() parameter.

Example Boot.ini

How do I work with “Advanced RISC Computer (ARC) names”? 

What are the two sections labeled [boot loader] and [operating systems] in the BOOT.INI (read only, system, hidden)?

1. The [boot loader] section supplies timeout interval after which the default operating system to load (defined in the default= line that follows timeout) loads automatically. *Windows NT usually boots from (boot loader) section.

2. The [operating systems] section supplies complete menu of operating system choices NTLDR displays after the program loads. You can disable the timer before it elapses by pressing any arrow or letter key on the keyboard. Then, you can wait as long as you like to make your menu selection. *Windows NT boots from (operating system) section if deliberate change to OS is made.

Note: You need to make changes in both especially if using disk mirroring or disk duplexing and one fails.

Remember

I. How do I determine if I use the Multi or SCSI parameter?

1. "SCSI" only applies to a SCSI drive whose onboard BIOS has been disabled (no BIOS translation capabilities).
2. If the NTBOOTDD.SYS file is on your system, use "SCSI".

If  neither is the case, use "multi."

II. How do I determine the SCSI or Multi number?

What is a disk controller - a chip and associated circuitry that is responsible for controlling a disk drive. There are different controllers for different interfaces. For example, an IDE interface requires an IDE controller and a SCSI interface requires a SCSI controller.

Which Disk Controller is the drive we are looking for attached to?

A. If there is only 1 Disk controller (multi or SCSI) = 0
B. If there are 2 Disk controllers (multi or SCSI) = 1 ; this is assuming the hard drive we are looking for is attached to the second controller. If the hard drive we are looking for is attached to the first disk controller (multi or SCSI) will = 0

III. How do I determine the rdisk and disk number?

Part 1

1. If we are using "multi", "disk" will always be 0
2. If we are using "scsi", "rdisk" will always be 0

Part 2

A. disk = SCSI bus ID (usually 0 to 6) when "SCSI" is chosen.
B. rdisk = LUN (SCSI logical unit number) or position in disk chain when "multi" is chosen. Usually
-The first hard disk = 0
-The second hard disk = 1
-The third hard disk = 2
-and so on unless specifically mentioned.

Odds and Ends

NTFS support:

When to use NTFS:

NTFS Notables

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I'm sorry, but I can't answer specific network-related, or exam-related questions.
Last Updated: August 6, 2001 Grant Wilson, Edmonton, AB Canada