HOW TO: Choose Between a Stripe Set, a Volume Set, a Stripe Set with Parity, and a Mirror Set

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SUMMARY

This step-by-step article describes how to choose between a stripe set, a volume set, a stripe set with parity, and a mirror set. This article includes a brief overview of each of these different volume types, and then it describes the criteria to help you decide which volume type to use in your Windows NT 4.0 environment.

NOTE: Windows NT 4.0 Workstation natively supports only stripe sets (RAID 0) and volume sets at the software level. Only Windows NT 4.0 Server natively supports all of these disk configurations.

Overview of Windows NT 4.0 Volume Types

This section describes the four different volume types that you can use in a Windows NT 4.0 environment.

Stripe Set

A stripe set (which is commonly known as RAID 0) consists of equal-sized areas of free space on at least 2 disks to as many as 32 disks that are combined in a single volume. When data is written to a stripe set, it is written evenly across all of the disks, one row at a time, in 64-kilobyte (KB) units. When you use a stripe set, you can store a larger amount of data than when you use a single disk. If the computer's disks are accessed simultaneously, a stripe set increases the speed of read actions and write actions to the disks because concurrent input/output (I/O) commands can be issued and processed on all disks simultaneously. A stripe set does not provide any fault tolerance because there is no data redundancy. The system and the boot partitions cannot be part of a stripe set.

Volume Set

A volume set consists of at least 2 areas and as many as 32 areas of unformatted free space on one or more disks that are combined into a single volume. These free spaces form one large logical volume set, which is treated as a single partition. The areas of free space do not have to be identical in size. When you use a volume set, data is written to one area at a time until no space remains on it, and then data is written to the next member of the volume set, and so on. When you use a volume set, you can store a larger amount of data than if you use a single disk volume. The volume set is extensible, which means that Windows can easily add data to the volume set. You do not increase speed performance if you use a volume set instead of a single disk volume. A volume set does not provide any fault tolerance because there is no data redundancy. The system and boot partitions cannot be part of a volume set.

Stripe Set with Parity

A stripe set with parity (which is commonly known as RAID 5) consists of equal-sized areas of free space on at least 3 disks and as many as 32 disks that are combined into a single, fault-tolerant volume. Like a stripe set and a volume set, a stripe set with parity provides a means to store a larger amount of data than a single disk can hold. Windows can read data from a stripe set with parity faster than from a mirror set. However, a stripe set with parity requires more system memory than a mirror set because of the parity calculations. Fault tolerance is achieved in a stripe set with parity because Windows NT writes parity information across each disk in the set. If a single disk in the set fails, data is not lost because data from the failed disk can be regenerated from the data and the parity information on each of the remaining disks in the set. (However, if a disk fails, the read performance slows considerably because data must be recovered by using parity information.) The system partition and the boot partitions cannot be part of a stripe set with parity.

Mirror Set

A mirror set (which is commonly known as RAID 1) is a set of two equal-sized partitions that are exact duplicates of each other. These two partitions are located on two separate disks. The term "disk mirroring" refers to mirror set use. When data is written to a mirror set, it is written to both partitions. A mirror set provides good read performance and good write performance; however, the mirror set does not read and write data as fast as a stripe set with parity. Of all the Windows NT 4.0 volume types, a mirror set provides the highest level of fault tolerance because data is duplicated in its entirety on to a separate disk. (It is also the most expensive volume type because disk space use is only 50 percent.) Any partition, including the boot or system partition, can be mirrored.

How to Choose a Volume Type for Your Windows NT 4.0 Environment

There are many factors that may influence your choice of volume type. The most important factor is fault tolerance, which is the ability of a computer or an operating system to respond to a catastrophic event, such as a power outage or a hardware failure, so that no data is lost and any work in progress is not corrupted. To decide the type of volume to use in your Windows NT 4.0 environment, you must decide if you require fault tolerance. If you require fault tolerance, follow the procedure that is described in the "How to Choose a Volume Type When You Require Fault Tolerance" section of this article. If you do not require fault tolerance, use the procedure that is described in the "How to Choose a Volume Type When You Do Not Require Fault Tolerance" section of this article.

How to Choose a Volume Type When You Require Fault Tolerance

To choose a volume type when you require fault tolerance:
  1. Decide if you want to use either a stripe set with parity or a mirror set (both volumes provide fault tolerance).

    The following table compares and contrasts these two volume types:
    Collapse this tableExpand this table
    Stripe Set with ParityMirror Set
    Supports FAT and NTFSSupports FAT and NTFS
    Cannot stripe the system or boot partitionCan mirror the system or boot partition
    Requires a minimum of 3 hard disksRequires 2 hard disks
    Has lower cost per megabyte (MB)Has higher cost per megabyte (MB)
    (50 percent disk utilization)
    Has moderate write performance
    Has excellent read performance
    Has good read and write performance
    Requires more system memory for parity
    calculations
    Uses less system memory
    Supports up to 32 hard disksSupports exactly 2 hard disks
    Is currently the most popular approach to
    fault tolerance
    Provides a higher level of fault tolerance
    than a stripe set with parity
  2. Determine your priorities. Is fault tolerance your highest priority (regardless of the cost)? Do you require only a modest amount of fault tolerance (for a more modest cost)? Is I/O performance (or speed) your highest priority?

    If fault tolerance is your highest priority, it is recommended that you use a mirror set for your Windows NT 4.0 environment. If either cost or speed is your highest priority, it is recommended that you use a stripe set with parity for your Windows NT 4.0 environment.

How to Choose a Volume Type When You Do Not Require Fault Tolerance

To choose a volume type when you do not require fault tolerance:
  1. Decide if you want to use either a stripe set or a volume set (both sets do not provide any fault tolerance).

    The following table compares the characteristics of these two volume types.

    NOTE: The following acronyms are used in this table:
    • IDE: Integrated development environment
    • SCSI: Small computer system interface
    • ESDI: Enhanced small device interface
    Collapse this tableExpand this table
    ConditionStripe SetVolume Set
    Can it be created on one physical drive?NoYes
    Can it contain the system or boot partition?NoNo
    What is the maximum number of areas (partitions)
    that can be combined?
    3232
    Must the areas combined be of the same size?YesNo
    Can it combine areas on different types of drives,
    such as SCSI, ESDI, and IDE?
    YesYes
    Is the area on one physical drive filled before the volume type
    starts to fill the next physical drive?
    NoYes
    Can it improve I/O performance?YesNo
    Is the volume type easily extended?NoYes
  2. Determine your priorities.

    Is I/O performance (speed) your highest priority? Or is extensibility your highest priority? The costs associated with a stripe set and a volume set are similar.

    If performance speed is your highest priority, it is recommended that you use a stripe set for your Windows NT 4.0 environment.

    If extensibility is your highest priority, it is recommended that you use a volume set for your Windows NT 4.0 environment.



REFERENCES

For more information about the Windows NT 4.0 volume types, see Modules 6 and 7 of Microsoft Official Curriculum, Course Number 922.

For additional information about how to configure a stripe set with parity, click the article number below to view the article in the Microsoft Knowledge Base:
316304 How to Configure a Stripe Set with Parity on a Windows NT Server 4.0 Computer
For additional information about how to configure a mirror set, click the article number below to view the article in the Microsoft Knowledge Base:
316311 How to Configure a Mirror Set on a Windows NT Server 4.0 Computer






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Article ID: 316298 - Last Review: October 31, 2006 - Revision: 1.1
APPLIES TO
  • Microsoft Windows NT Workstation 4.0 Developer Edition
  • Microsoft Windows NT Server 4.0 Standard Edition
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