Microsoft Windows XP Professional Administrators Guide

Windows XP Professional supports two different types of disks, basic and dynamic. All Microsoft operating systems until Windows 2000 supported only basic drives. Windows XP Professional automatically treats all new drives as basic drives. Basic drives can be accessed by any Windows operating system and are required to support dual-boot configurations.

Basic disks support the allocation of an entire drive or just a portion of the drive to the formation of a partition. Partitions are then assigned a file system and are used to install operating systems and to store data. Windows XP Professional supports the following types of partitions:

• Primary.A self-contained area of disk storage, which is formatted using a single file system and assigned a drive letter.

• Extended.A self-contained area of disk space that can be further subdivided into multiple logical drives, each of which can be assigned its own drive letter. The partition itself does not receive a drive letter assignment.

Windows XP's basic drives permit the establishment of up to four primary partitions on a single disk drive or the creation of three primary partitions and one logical partition, which can then be further subdivided into logical drives. Reasons for partitioning disk drives include:

• Creating separate partitions for the operating system and data, which prevents the computer from crashing should the data partition run out of storage

• Creating a separate partition for each operating system in a dual-boot configuration

• Subdividing a large disk drive into multiple partitions when using the FAT file system in order to work around FAT's 2 GB maximum partition size limitation

• Establishing a special recovery partition on which administrators can install a second instance of Windows XP Professional for the purpose of booting and troubleshooting in emergency situations

Dynamic drives provide more features than basic disks. The basic unit of storage in a dynamic disk is the volume (as opposed to a partition). Whereas basic drive partitions are limited to 2 terabytes, dynamic drive volumes can span multiple disk drives and exceed this limit. Dynamic disks also support the establishment of mount points, which allow a new disk to be mounted or added as a logical folder to an existing volume, thus logically extending the size of the drive by spanning it over two physical drives. Windows XP allows disk spanning to occur over as many as 32 disk drives.

Dynamic drives allow for the creation of all the following volume types:

• Simple.Creates a dynamic disk using only contiguous storage space provided from a single disk drive. Simple volumes are appropriate for the average user.

• Striped.Creates a dynamic disk by allocating a portion of contiguous space from two or more disk drives into a single logical volume. All data is evenly written to each drive in the striped volume to improve overall performance. Striped volumes can be used to provide high-end workstations with better performance and additional storage.

• Spanned.Creates a dynamic disk by allocating a portion of contiguous space from two or more disk drives into a single logical volume. All data is written to the first drive in the set until it fills up and then is written to the next drive in the set. This option does not provide a performance improvement like the striped volume. Use spanned volumes to provide users who have exhausted the available storage space on their local disk drive with additional storage, without adding the complicity of making them work with a second drive letter.

Basic partition and dynamic volumes cannot be established on the same partition. However, if a computer has more than one hard drive, each of these options can be used on a separate drive if desired. Dynamic drives are limited to traditional hard disk drives. Therefore, they cannot be used on any of the following storage devices:

• USB drives

• IEEE 1934 drives

• Removable disk drives

In addition, Windows XP will not allow dynamic drives to be set up on a portable laptop computer. All of these factors combine to limit the deployment scenarios in which dynamic disks can be used.

By default, Windows XP sets up all disks as basic disks. A basic disk can be converted to a dynamic disk without the loss of any data. To convert the dynamic disk back to a basic disk, administrators must back up all the data stored on the disk, delete all volumes on the dynamic disk, convert it to a basic disk, format it with a file system, and finally restore the data. Unless a basic disk contains Windows XP's system or boot files, it can be converted to a dynamic disk without requiring a restart of the system.