CAP Theorem is comprised of three technical terms:
C – Consistency (All nodes see the data in homogeneous form i.e. every node has the same knowledge of data at any instant of time)
A – Availability (A guarantee that every request receives a response which may be processed or failed)
P – Partition Tolerance (The system continues to operate even if a message is lost or part of the system fails)
Any system which satisfies two out of these three properties is a distributed system.
Talking about Hadoop , it supports the Availability and Partition Tolerance property. The Consistency property is not supported because only namenode has the information of where the replicas are placed. This information is not available with each and every node of the cluster.