Sabtu, 19 Desember 2015

Sistem Terdistribusi : Exercises For Chapter 2



Exercises 2.16

Suppose that a basic disk read can sometimes read values that are different from those written. State the type of failure exhibited by a basic disk read. Suggest how this failure may be masked in order to produce a different benign form of failure. Now suggest how to mask the benign failure.

Answer :

The basic disk read exhibit arbitrary failures.
This can be masked by using a checksum on each disk block (making it unlikely that wrong values will go undetected) - when an incorrect value is detected, the read returns no value instead of a wrong value - an omission failure.
The omission failures can be masked by replicating each disk block on two independent disks. (Making omission failures unlikely).