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.

Question

What will be an ideal response?

Answer 1

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).