Disk Striping And Disk Striping With Parity In Windows NT

• Microsoft Windows NT operating system version 3.1
• Microsoft Windows NT Advanced Server version 3.1

SUMMARY

Windows NT and Windows NT Advanced Server disk striping (RAID Level 0) creates a disk file system called a stripe set by dividing data into blocks and spreading them in a fixed order across all disks in an array. By adding data to all partitions in the set at the same rate, disk striping offers the best performance of all Windows NT disk management strategies.

Windows NT Advanced Server allows you to establish fault tolerant disk striping with parity (RAID Level 5), which stores parity information along with striped data on different disks in the array for redundancy. Disk striping with parity is available only with Windows NT Advanced Server, not with Windows NT.

The rest of this article describes disk striping with and without parity in Windows NT and Windows NT Advanced Server.

MORE INFORMATION

Disk Striping in General--With or Without Parity

• Stripe sets are user-transparent: when they are created, all partitions are assigned the same drive letter.



• All partitions in a stripe set are the same size. If you select free disk areas of different sizes when you create a stripe set, no stripe will be larger than the smallest free disk area.



• Stripe sets must be created from free disk space; they cannot be used on existing partitions.



• Stripe sets are file system independent and can be formatted with any Windows NT disk file system.



• Disk Administrator assigns the same color to all stripe sets. The status bar in the lower left corner of the Disk Administrator window tells whether a stripe set has parity or not.



• Only the Windows NT Advanced Server installation that created the stripe set will normally recognize it; other operating systems will not. MS-DOS identifies stripe set partitions as Non-DOS. Other installations of Windows NT and Windows NT Advanced Server identify stripe set partitions as being of "Unknown" file system type.



• An installation of Windows NT or Windows NT Advanced Server can restore disk configuration information and thereby recognize a stripe set created by a different installation on the same machine. See page 529 of the "Windows NT Advanced Server System Guide" for more information.

Disk Striping Without Parity

• Disk striping without parity provides no fault tolerance; if one disk in the stripe is bad or damaged, the entire disk stripe is lost.



• A stripe set can be created on as few as 2 and as many as 32 disks. Only one stripe on a stripe set can be located on each physical disk.



• Disk striping offers the best performance of all Windows NT disk management strategies.



• Disk Administrator assigns the same color to all stripe sets. For a stripe set without parity, the status bar in the lower left corner of the Disk Administrator window says simply "Stripe set #X." parity).



• For information on creating and managing a stripe set, consult the "Windows NT System Guide" or "Windows NT Advanced Server System Guide."

Disk Striping With Parity

• A stripe set with parity can be created on as few as 3 and as many as 32 disks. Only one stripe on a stripe set with parity can be located on each physical disk.



• The amount of disk space used to store parity information is always equal to the size of one of the partitions in the set. For example, if a stripe set with parity is created on five disks, each with a 500 MB partition used for the stripe, 500 MB is used for parity information and 2000 MB is available for data storage.



• Regardless of how many disks are used in a stripe set with parity, data is recoverable only if no more than one disk is lost. If two or more disks are lost, the data is unrecoverable.



• The fault tolerance driver (FTDISK.SYS) makes the loss of one partition in a stripe set with parity invisible--you can read and write to a set with a lost partition as if it were healthy. But the stripe set is no longer fault tolerant: the loss of any remaining partitions will result in an unrecoverable loss of all data in the stripe set.



• The status bar in Disk Administrator indicates stripe set condition. When a partition in the set is selected, Disk Administrator displays information about the set in the lower left corner of the window, as in: "Stripe set with parity #0 [HEALTHY]" Other status indicators include:
  
  [NEW]: this appears right after the stripe set has been created in Disk Administrator, and before the shutdown of the system and the actual generation of the set.
  
  [INITIALIZING]: this appears during stripe set generation.
  
  [RECOVERABLE]: this appears when one of the partitions in the set has been lost but the other partitions are undamaged, or when one partition in the set is not synchronized with the others.



• Disk Administrator assigns the same color to all stripe sets. To tell which have parity, look at the status bar in the lower left corner of the Disk Administrator window. For a stripe set with parity, the description says "Stripe set with parity #X."



• For information on creating and managing a stripe set with parity, consult the "Windows NT Advanced Server System Guide" and the "Windows NT Concepts and Planning Guide."

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