From CS552 Course Wiki: Spring 2017

Main: Disks-1

Disk Storage

Mean time to recovery (MTTR): In RAID that include redundancy for reliability, this is the time following a failure to restore an array to its normal failure-tolerant mode of operation. This includes time to replace a failed disk mechanism as well as time to re-build the failed disk. (i.e. to replicate data for redundancy).

Here, the devices themselves determine which of them has the highest priority. Each device has a bus_request line or lines on which it places a code identifying itself. Each device examines the codes for all the requesting devices, and determines whether or not it is the highest priority requesting device.

  • Collision Arbiter: This employs backoff method in case of bus conflicts. The employed backoff methods can be exponential.
  • Software Interface for I/O
  • ISA Level
  • System Software
  • Processor - Device interaction: The job of a processor entails how to initiate communication with the device, receive communications from the device.
    • Initiate Communication: Memory mapped I/O:- Set of addresses in memory used to communicate with the device.
    • Receive Communication: Interrupts and Polling.
    • DMA: Transfer without continuous processor involvement. The processor hands off the source, dest address and number of bytes to the DMA controller. The DMA controller performs the operations and interrupts the processor on completion. The DMA is also memory mapped.
  • System Software Support
    • Required for protection and security issues.
    • Make an easy interface for use.
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Page last modified on April 29, 2008, at 12:06 PM