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).
