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Q162846: Preparing to Create or Modify a Fault Tolerant Set

Article: Q162846
Product(s): Microsoft Windows NT
Version(s): WinNT:3.5,3.51,4.0
Operating System(s): 
Keyword(s): kbtool
Last Modified: 08-AUG-2001

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The information in this article applies to:

- Microsoft Windows NT Workstation versions 3.5, 3.51, 4.0 
- Microsoft Windows NT Server versions 3.5, 3.51, 4.0 
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SUMMARY
=======

This article provides some basic procedures and a checklist for creating and
modifying a fault tolerant set. For this article, a fault tolerant set includes
a stripe set, stripe set with parity, volume set, and disk mirror/duplex.

Basic Procedures
----------------

1. To create a fault tolerant set, perform a full backup of all data. Back up
  anything that cannot be reinstalled and back up any data that you cannot
  regenerate on physical media, other than the drives you are going to use.

2. Because information about fault tolerant sets is kept in the registry, it is
  preferable that you back up the disk key in the system hive separately. You
  can easily do this by using the Save option of the Configuration entry under
  the Partition menu in Disk Administrator. This option will copy the disk key
  in an uncompressed format to a floppy disk. The disk key keeps the Disk
  Signature and any fault tolerant set information of the drives in your
  system.

  NOTE: It does not save the master boot record, boot sector, or any partition
  information. You may also want to use RDISK to back up the rest of the
  registry including the entire SYSTEM hive.



3. All third-party services and drivers need to be stopped through Services tool
  and Devices tool in Control Panel. These services may not only be limited to
  virus scanners, backup agents, and network services, but may extend to
  utilities that may maintain open files, or access system services directly
  (low-level hardware access such as Compaq Insight Manager). Also,
  applications such as Microsoft Exchange Server and SQL Server, among others
  that perform low-level disk I/O, need to be stopped.

  The drive needs to be checked for file structure and physical corruption with
  a utility such as CHKDSK. For CHKDSK use the /r to search for bad sectors and
  /f to fix any errors it finds. If possible, use the SCSI controller low-level
  media test to run a nondestructive test (consult your hardware vendor for
  details and availability).

For additional information, please see the following articles in the Microsoft
Knowledge Base:

  ARTICLE-ID: Q100110
  TITLE : Overview of Redundant Arrays of Inexpensive Disks (RAID)

  ARTICLE-ID: Q114872
  TITLE : Restoring Disk Configuration Information

Stripe Sets
-----------

Stripe sets offer no data redundancy, unlike striping with parity. All data is
lost in the set if one drive fails in a stripe set. Better performance usually
results because of the ability to read and write to several drives
simultaneously. To do this, the drives and controller must support the read and
write request simultaneously. In general, most SCSI controllers and drives allow
this, while IDE controllers and drives only allow one device per channel at a
time to accept read and write requests. Making a stripe set out of IDE drives
will not improve performance.

Stripe sets with parity offer data redundancy. They maintain a fairly high level
of performance. Read performance matches a stripe set without parity. When
writing data, however, everything is written twice -- once to the disk and once
to the parity strip. The pagefile should not be placed on a stripe set with
parity because redundant data is written and performance degrades. After a
stripe set is created, it cannot be enlarged or extended without backing up the
data and reformatting the set. You cannot incorporate the Windows NT system or
boot files into a stripe set.

For additional information, please see the following articles in the Microsoft
Knowledge Base:

  ARTICLE-ID: Q113933
  TITLE : Disk Striping and Disk Striping with Parity in Windows NT

  ARTICLE-ID: Q108082
  TITLE : Windows NT Cannot Regenerate Stripe Set with Parity

Volume Set
----------

Volume sets offer no data redundancy but allow you to span multiple drives, and
to assign them one drive letter. When you use NTFS on a volume set, it is
possible to add another drive to volume set without formatting the drive. FAT
does not allow extending the drive without reformatting and restoring from a
backup. When extending a volume set, take the same precautions as when you
create any other fault tolerant set.


For additional information, please see the following article in the Microsoft
Knowledge Base Article related to Volume Sets:

  ARTICLE-ID: Q113503
  TITLE : Overview of Disk Volume Sets in Windows NT

Disk Mirror/Duplex
------------------

Disk mirroring and disk duplexing offer full data redundancy under Windows NT
Server. The difference between the two is that mirroring assumes you have two
hard drives and one controller, while duplexing has a controller for each hard
drive. Duplexing provides maximum protection if a controller or a hard drive
fails. The type and size of your hard drive does not matter, but there must be
enough free space available on the shadow drive. When duplexing, drive
translation can be an issue on SCSI drives. When the BIOS is enabled on a SCSI
controller, the drive translation is done by the BIOS. For controllers not under
BIOS control, Windows NT defaults to 64 heads and 32 sectors per track. This
happens because Windows NT cannot read the translation scheme from the disabled
BIOS. An issue arises when there are two identical controllers and two identical
drives, with two different sizes under Disk Administrator. In this situation,
even if the mirror can be established, recovery in the event of failure may be
extremely difficult.

For additional information, please see the following articles in the Microsoft
Knowledge Base:

  ARTICLE-ID: Q114779
  TITLE : Overview of Disk Mirroring (RAID Level 1) in Windows NT

  ARTICLE-ID: Q113977
  TITLE : Booting From Mirror After Primary Partition Is Lost

  ARTICLE-ID: Q141702
  TITLE : How to Recover Mirroring Windows NT Using IDE devices

  ARTICLE-ID: Q161563
  TITLE : How Windows NT Handles Drive Translation

  ARTICLE-ID: Q148425
  TITLE : Duplexed Mirror Fails with Insufficient Space

  ARTICLE-ID: Q172912
  TITLE : Windows NT May Appear to Hang When a Mirrored IDE Drive Fails

MORE INFORMATION
================

Windows NT Server support for RAID is software based; information about the
configuration is kept in the registry. Hardware-based RAID has many advantages
over software-based RAID, such as support for hot swapping of hard drives.
Hardware-based RAID provides better performance because it runs independently of
the operating system and does not need to scan a series of drivers. The
operating system can be placed on a hardware-based RAID because the array is
built in the controller BIOS, and not by a driver that the operating system
supplies.

Compaq is independent of Microsoft; we make no warranty, implied or otherwise,
regarding this companies product's performance or reliability.

For additional information, please see the following article in the Microsoft
Knowledge Base:

  ARTICLE-ID: Q96735
  TITLE : Hardware/Software Requirements for Fault Tolerance

Additional query words: prepare harddrive

======================================================================
Keywords          : kbtool 
Technology        : kbWinNTsearch kbWinNTWsearch kbWinNTW400 kbWinNTW400search kbWinNT351search kbWinNT350search kbWinNT400search kbWinNTW350 kbWinNTW350search kbWinNTW351search kbWinNTW351 kbWinNTSsearch kbWinNTS400search kbWinNTS400 kbWinNTS351 kbWinNTS350 kbWinNTS351search kbWinNTS350search
Version           : WinNT:3.5,3.51,4.0
Issue type        : kbinfo

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