DOCUMENT:Q170921  10-AUG-2001  [winnt]
TITLE   :Scaling Windows NT Server Storage and Fault Tolerance
PRODUCT :Microsoft Windows NT
PROD/VER:winnt:3.5,3.51,4.0
OPER/SYS:
KEYWORDS:kbsetup kbhowto

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The information in this article applies to:

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

This article discusses using Windows NT Server's software fault tolerance
capabilities to scale invested hardware to meet current and future storage
demands. Note that these capabilities are not as fast or dependable as hardware
fault tolerance but can help extend existing hardware functionality.

This article is primarily for systems administrators who have installed systems
that use hardware RAID arrays and who want to combine two or more hardware RAID
arrays as one functional logical drive to expand space, improve performance, and
extend the usefulness of existing hardware investments.

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

Scaling multiple RAID arrays can exceed the bandwidth of the BUS that the SCSI
controllers are using, so knowledge of SCSI capacity planning is assumed in this
article.

For more information regarding SCSI capacity planning, please see the Microsoft
TechNet article "SCSI: Hardware Performance Considerations for Win95/NT" under
Hardware/Hardware Products Architecture.

IMPORTANT! Introducing Windows NT's software fault tolerance requires that you
keep a valid copy of the DISK key by either having current backups of the
registry and a recent emergency repair disk, or using the Disk Administrator's
Partition/Configuration/Save option to set up a valid DISK key backup.

SCALING METHODS:

NT Mirroring Hardware Stripe Sets (sometimes referred to as RAID 10)
--------------------------------------------------------------------

Disk0---(Stripe)----DiskX
      ^
      |   (mirrored)
      v
Disk0---(Stripe)----DiskX

Pros: The fastest RAID array method; excellent read and write speed.

Cons: Mirroring provides the minimum FT required. Any corruption of the data may
replicate to the shadow set. This provides no integrity protection for the drive
arrays because they are running a stripe set underneath. Any drive failure would
render the one of the arrays offline.

H/W RAID-5 Arrays in NT Volume Set
----------------------------------

Disk0---Disk1---Disk2---DiskX (Hardware RAID 5 array)  member-1
      (NT Volume Set)
Disk0---Disk1---Disk2---DiskX (Hardware RAID 5 array)  member-2

Pros: Allows very large logical drives with RAID 5 fault tolerance underneath to
protect the volume set. Allows two dissimilar RAID 5 arrays to be grouped
together. This allows you to concentrate on the size of the logical driver
rather than on performance.

Cons: Performance of the RAID arrays is not combined as RAID 10. This gives the
least-optimal performance of all the configurations. Additionally, the logical
or physical loss of one member results in the total loss of the entire volume
set.

NT Mirroring of H/W RAID-5 Sets
-------------------------------

Disk0---Disk1---Disk2---DiskX (Hardware RAID-5 array)
      ^
      |   (mirrored)
      v
Disk0---Disk1---Disk2---DiskX (Hardware RAID-5 array)

Pros: Very good read performance; good write performance. Both the data and drive
arrays have fault tolerance.

Cons: Any corruption of the data could be replicated to the shadow drive. Very
costly due to duplicate hardware requirements.

NT RAID-5 on Multiple H/W RAID-5 Arrays
---------------------------------------

Disk0--Disk1--DiskX (H/W RAID-5 array)\ 
Disk0--Disk1--DiskX (H/W RAID-5 array) |-RAID-5 created in Disk Admin.
Disk0--Disk1--DiskX (H/W RAID-5 array)/ 

Pros: Excellent read speeds; good write speed. This is the one of the best
combinations of speed and security. The array and the data have the benefit of
RAID protection.

Cons: The number of h/w RAID arrays required to make this efficient is a
disadvantage. Three RAID-5 arrays in a soft RAID-5 would lose one-third total
space to parity. Generally desirable would be four or five arrays to make the
parity space required more reasonable (one-fourth or one-fifth total space).


Additional query words: prodnt scale fault tolerance

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Keywords          : kbsetup kbhowto 
Technology        : kbWinNTsearch kbWinNT351search kbWinNT350search kbWinNT400search kbWinNTSsearch kbWinNTS400search kbWinNTS400 kbWinNTS351 kbWinNTS350 kbWinNTS351search kbWinNTS350search
Version           : winnt:3.5,3.51,4.0

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