MGMT 1050 Lecture Notes - Lecture 24: Disk Controller, Disk Array, Conventional Memory
MGMT 1050 Lecture 24 Notes – Disk Arrays
Introduction
• As you now know from this chapter, the disk controller identifies the disk block to be
located, moves the head to the correct track, then reads the track data until it
encounters the header for the correct block.
• Assuming that it is performing a read, it then transfers the data from the disk to a
buffer.
• From the buffer, the data is transferred to conventional memory using DMA.
• Once the DMA transfer is complete, the disk controller notifies the CPU with a
completion interrupt.
• In larger computer environments, with mainframe computers or large PCs that provide
program and data storage facilities for a network, it is common to group multiple disks
together.
• Such a grouping of two or more disk drives is called a disk array or a drive array.
• A disk array can be used to reduce overall data access time by sharing the data among
multiple disks and also to increase system reliability by providing storage redundancy.
• The assumption made is that the number of blocks to be manipulated at a given time is
large enough and important enough to justify the additional effort and additional space
requirements.
• One useful type of disk array is known as RAID, which stands for Redundant Array of
Inexpensive Disks.
• Soe people say ‘edudat Array of Idepedet Disks.
• There are two standard methods of implementing a disk array.
• One is known as a mirrored array, and the other as a striped array.
• A mirrored array consists of two or more disk drives.
• In a mirrored array, each disk stores exactly the same data.
• Moves the head to the correct track, then reads the track data until it encounters the
header for the correct block.
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