As with new technology, issues arise when similar terminology is used with seemingly similar technologies. HDFS vs. Cloud Object Storage is one of those cases, but HDFS and Cloud Object Storage are not necessarily comparable.
HDFS is a distributed file system for storing large data, within a file hierarchy. Object Storage, like Amazon’s S3, is a strategy for storing data as objects, and managing those objects with referent metadata, typically to store voluminous unstructured data. While they both deal with storing data in different storage architectures, the functionality of Hadoop makes it far more complex.
Another significant difference is that HDFS follows the premise of moving compute power to where data is, such as the DataNode, where processing can occur in order to reduce network congestion instead of sending data away to be computed. Computation is strictly not included in object storage, which only deals with storing data as objects.