Volume Summary

Use dynamic volumes on dynamic disks to take advantage of advanced disk configurations that provide for increased performance or fault tolerance. The following table describes the dynamic volume types:

Volume Type Description
Simple A simple volume contains a single, contiguous block of space from a single hard disk.

  • You can extend a simple volume onto the same disk, as long as the disk space is contiguous.
  • Simple volumes do not provide any performance or fault tolerance advantages.
Spanned A spanned volume combines areas from two or more disks into one storage unit. The primary purpose of a spanned volume is to add more storage space to an existing volume. A spanned volume:

  • Fills the first area, then the second, and so on.
  • Does not provide fault tolerance. If one hard disk fails, you lose all data.
  • Cannot contain system or boot files.
  • Can include space from between 2 and 32 physical disks. The amount of space used on each disk can be different.
  • Has no overhead; all disk space is available for storing data.
Striped (RAID 0) A striped volume breaks data into units and stores the units across a series of disks. When you save a single file on a striped volume, pieces of the file will be found in all disks in the array. Striped volumes:

  • Use two or more disks. The amount of space used on each disk must be the same.
  • Provide an increase in performance. Multiple disk controllers read and write data at the same time, reducing the overall time to read or write any file.
  • Do not provide fault tolerance. A failure of one disk in the set means all data is lost.
  • Have no overhead–all disk space is available for storing data.
Striped with parity (RAID 5) A striped volume with parity combines disk striping across multiple disks with parity for data redundancy. Parity information is stored on each disk. If a disk fails, its data can be recovered using the parity information stored on the remaining disks. RAID 5 volumes:

  • Require a minimum of three disks, with equal space being used on each disk.
  • Provide fault tolerance. Data is available even if one disk in the set fails, though performance is significantly impaired.
  • Provide an increase in performance (although the performance is not as good as that of a striped volume).
  • Have an overhead of one disk in the set for parity information.
    • A set with 3 disks has 33% overhead.
    • A set with 4 disks has 25% overhead.
    • A set with 5 disks has 20% overhead.
Mirrored
(RAID 1)
A mirrored volume stores two copies of each file, with one copy on each disk or disk set. Mirrored volumes:

  • Require two disks.
  • Mirror only volumes.
  • Require that a mirror of a volume be the same size as the volume.
  • Provide the only type of fault tolerance for the operating system.
  • Provide fault tolerance. If one disk fails, data is preserved on the other disk, and the system switches immediately from the failed disk to the functioning disk to maintain availability.
  • Do not increase performance.
  • Have a 50% overhead. Data is written twice, meaning that half of the disk space is used to store the second copy of the data.

Disk duplexing is a type of mirroring. Disk duplexing uses two hard drives and two separate disk controllers. Disk duplexing eliminates the single point of failure when a single disk controller is used.

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