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Hard Disk Management in Windows XP- Dynamic Disks

We continue the discussion of hard drive management begun on previous pages where we looked at Properties Sheets and the Disk Management Console. Beginning with Windows 2000 and continuing in Windows XP Professional, Microsoft introduced a new way of organizing the structure of hard drives called "dynamic disks". We will briefly consider some aspects of this different approach to storing information. The concepts that will be discussed apply only to Windows Professional systems. Windows Home does not support dynamic disks.

Basic disks

The type of disk configuration still mostly used in home systems is referred to as a basic disk. Files are stored either on any available space on a given hard drive or are stored in segments of the hard drive designated as partitions. Within a given partition the storage space consists of contiguous areas. Individual partitions are also usually contiguous to one another on a given hard drive. Files are always located in a particular, well-defined physical area of a disk. Any change in the way space is allocated on a disk or partition requires rebooting and requires special software to preserve data or files.

Dynamic disks

In dynamic disks, space allocations can be changed by the operating system. (Note: Dynamic disks cannot be assigned to removable media or USB connected disks.) Units of storage space that are assigned letter designations are no longer limited to a given hard drive device or physically contiguous areas and are referred to as volumes. The contents of a file can be split across physically distinct hard drives. Here are some different types of volume.

A simple volume uses space on a single drive. Unlike the older type of space allocation called a partition, however, the space in a simple volume does not have to be contiguous but can be concatenated from physically separate parts of the drive. The total space is assigned a single volume letter and is accessed as if it were a single block.
In a spanned volume, regions on more than one physically distinct disk have been joined to form a single volume. This type of setup can be convenient if you are running low on available space in a volume. You can add another drive and simply add to the volume as much of the capacity of the new drive as is desired. Note, however, that if one disk drive fails, everything is lost.
Striped or RAID-0
A striped or RAID-0 volume also contains data stored across two or more physical drives. (RAID stands for Redundant Array of Independent Disks.) Data is stored by allocating it alternately and evenly to each of the disks. The purpose is to speed up disk throughput. If one of the drives fails, however, everything is lost. In addition to being supported by Windows XP, disk controller hardware may also support this type of configuration.
Mirrored or RAID-1
A mirrored volume consists of data on one disk and a a duplicate of the data on another disk. Programs see only a single volume. Windows keeps the two drives synchronized and if one drive fails the data are available from the other drive. This setup is used where it is important to have a fault-tolerant system. There are even more elaborate systems for fault-tolerance such as RAID-5 involving three disks, but these require the Windows 2000 Server, Windows 2003 Server, or similar operating system.

The Disk Management Console can be used in Windows XP Professional to configure various dynamic disk setups. There is a Wizard for converting simple disks to dynamic. For details see this Microsoft reference or this tutorial.

Mounting a disk in a folder

The ability to mount or graft a drive into a folder on another drive is not new to UNIX users but many users of Windows are unaware of this feature of systems with NTFS. Instead of assigning a letter to a drive and treating it as a separate volume, you can allocate the space on the drive to an existing (but empty) folder on another drive. Note that this procedure results in one very large folder whereas disk spanning results in an enlargement of the entire volume.


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