Sunday, 2 December 2012

Exam preparation (70-687) - Types of Dynamic volumes

Types of Dynamic Volumes

A dynamic volume is a volume that is created on a dynamic disk. Dynamic volume types include simple, spanned, and striped volumes. Windows Server 2003 also supports mirrored and RAID-5 volumes, which are fault tolerant. Fault tolerance is the ability of computer hardware or software to make sure that your data is still available, even if there is a hardware failure.

Simple Volumes

Simple volumes are the dynamic-disk equivalent of the primary partitions and logical drives found on basic disks. When creating simple volumes, keep these points in mind:
  • If you have only one dynamic disk, you can create only simple volumes.
  • You can increase the size of a simple volume to include unallocated space on the same disk or on a different disk. The volume must be unformatted or formatted by using NTFS. You can increase the size of a simple volume in two ways:

    • By extending the simple volume on the same disk. The volume remains a simple volume, and you can still mirror it.
    • By extending a simple volume to include unallocated space on other disks on the same computer. This creates a spanned volume.

      Note : If the simple volume is the system volume or the boot volume, you cannot extend it.

Spanned Volumes

Spanned volumes combine areas of unallocated space from multiple disks into one logical volume. The areas of unallocated space can be different sizes. Spanned volumes require two disks, and you can use up to 32 disks. When creating spanned volumes, keep these points in mind:
  • You can extend only NTFS volumes or unformatted volumes.
  • After you create or extend a spanned volume, you cannot delete any portion of it without deleting the entire spanned volume.
  • You cannot stripe or mirror spanned volumes. For more information about striped or mirrored volumes, see “Striped Volumes” or “Mirrored Volumes” later in this section.
  • Spanned volumes do not provide fault tolerance. If one of the disks containing a spanned volume fails, the entire volume fails, and all data on the spanned volume becomes inaccessible. The reliability for a spanned volume is less than the least reliable disk in the set.

Striped Volumes

Striped volumes improve disk input/output (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 two or more disks. In Windows Server 2003, the size of each stripe is 64 kilobytes (KB) and cannot be changed.
Striped volumes cannot be extended or mirrored and do not offer fault tolerance. If one of the disks containing a striped volume fails, the entire volume fails, and all data on the striped volume becomes inaccessible. The reliability for the striped volume is less than the least reliable disk in the set.

Mirrored Volumes

A mirrored volume is a fault-tolerant volume that provides a copy of a volume on another disk. Mirrored volumes provide data redundancy by duplicating the information contained on the volume. The two disks that make up a mirrored volume are known as mirrors. Each mirror is always located on a different disk. If one of the disks fails, the data on the failed disk becomes unavailable, but the system continues to operate by using the unaffected disk.
Mirrored volumes are available only on computers running the Windows 2000 Server family or Windows Server 2003.

RAID-5 Volumes

A RAID-5 volume is a fault-tolerant volume that stripes data and parity across three or more disks. Parity is a calculated value that is used to reconstruct data if one disk fails. When a disk fails, Windows Server 2003 continues to operate by recreating the data that was on the failed disk from the remaining data and parity. RAID-5 volumes are available only on computers running the Windows 2000 Server family or Windows Server 2003.

source : http://technet.microsoft.com/en-us/library/cc737048%28v=ws.10%29.aspx

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