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SAN School Answer #6

SAN School Answer #6

SAN School Answer #6

Question #6

This is a way of storing the same data in different places (redundantly) on multiple hard disks.

a. data mining
b. disk duplexing
d. data splitting
e. virtualization

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RAID (redundant array of independent disks; originally redundant array of inexpensive disks) is a way of storing the same data in different places (thus, redundantly) on multiple hard disks. By placing data on multiple disks, I/O operations can overlap in a balanced way, improving performance. Since multiple disks increases the mean time between failure (MTBF), storing data redundantly also increases fault-tolerance.

A RAID appears to the operating system to be a single logical hard disk. RAID employs the technique of striping, which involves partitioning each drive's storage space into units ranging from a sector (512 bytes) up to several megabytes. The stripes of all the disks are interleaved and addressed in order.

In a single-user system where large records, such as medical or other scientific images, are stored, the stripes are typically set up to be small (perhaps 512 bytes) so that a single record spans all disks and can be accessed quickly by reading all disks at the same time.

In a multi-user system, better performance requires establishing a stripe wide enough to hold the typical or maximum size record. This allows overlapped disk I/O across drives.

For more on RAID, see also:

  • RAID reliability
  • Selecting the proper RAID level for your business intelligence workload
  • Setting up databases, indexes and log files

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  • This was last published in August 2003

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