Final answer:
Cassandra utilizes a Bloom Filter to efficiently ascertain if an index entry might be present on the disk, effectively minimizing unnecessary I/O operations.
Step-by-step explanation:
Cassandra searches the Bloom Filter to determine the approximate location of the index entry on the disk. Cassandra uses a Bloom Filter as a probabilistic data structure to test whether an element might be in a set before attempting to retrieve it from the disk. If the Bloom Filter indicates that the element is not in the set, Cassandra knows not to attempt a disk read, which saves I/O operations. However, Bloom filters have a certain probability of offering false positives, which means they can indicate that an element is a member of the set when it is not. Still, this rate is manageable, and the benefits of saving I/O outweigh the risks associated with these false positives. This characteristic makes Bloom Filters a valuable tool in systems like Cassandra for quickly narrowing down searches without intensive disk access.