Striped Volumes

Windows 2000 Server and Windows 2000 Professional provide software support for striped volumes, which are configured by using Disk Management. Striped volumes improve I/O performance by distributing I/O requests across disks. Striped volumes are composed of stripes of data of equal size written across each disk in the volume. They are created from equally sized, unallocated areas on up to 32 physical disks. For Windows 2000, the size of each stripe is 64 kilobytes (KB).

Conceptually, a striped volume is similar to a table in a document, where a disk is a column and a stripe is one of the entries in the table. A stripe includes all of the entries in one row. Table 11.3 illustrates the structure of a striped volume and shows the order in which data is written to the striped volume.

Table 11.3 Structure of a Striped Volume

In the preceding table, stripe 1 consists of the four stripes that are the first block on each of the four disks. Stripe 5 is made up of the stripes that are the last block on each disk.

When you write data to a striped volume, the data is written across the stripes in the volume. Thus, using Table 11.3 as an example, a file of 325 KB could occupy the following space:

• 64 KB on stripe 1 of disk 1
• 64 KB on stripe 1 of disk 2
• 64 KB on stripe 1 of disk 3
• 64 KB on stripe 1 of disk 4
• 64 KB on stripe 2 of disk 1
• 5 KB on stripe 2 of disk 2

The physical disks in a striped volume do not need to be identical, but there must be unused space available on each disk that you want to include in the volume. You cannot increase the size of a striped volume after it is created. To change the size of a striped volume, you must first complete the following steps:

• Back up the data.
• Delete the striped volume by using Disk Management.
• Create a new, larger, striped volume by using Disk Management.
• Restore the data to the new striped volume.

Striped volumes do not contain redundant information. Therefore, the cost per megabyte on a striped volume is identical to that for the same amount of storage configured from a contiguous area on a single disk. If one disk fails, the whole striped volume fails and no data can be recovered. The reliability for the striped volume is less than the least reliable disk in the set.

Stripe sets are used for performance reasons. In general, striped volumes work well when you need to distribute I/O operations. Access to the data on a striped volume is usually faster than access to the same data would be on a single disk, because the I/O is spread across more than one disk. Therefore, Windows 2000 can be seeking on more than one disk at the same time, and can have simultaneous read or write operations occurring.

A striped volume works well in the following situations:

• When users need rapid read access to large databases or other data structures.
• When storing program images, dynamic-link libraries (DLLs), or run-time libraries for rapid loading. Operating systems such as Windows 2000 that use memory mapped images can benefit from using striped volumes.
• When collecting data from external sources at very high transfer rates. This is especially useful when collection is done asynchronously.
• When multiple independent applications require access to data stored on the striped volume. When the operating system supports asynchronous multithreading, which helps load balance disk read and write operations.

© 1985-2000 Microsoft Corporation. All rights reserved.