Various Filesystems in Hadoop

Hadoop is an open-source software framework written in Java along with some shell scripting and C code for performing computation over very large data. Hadoop is utilized for batch/offline processing over the network of so many machines forming a physical cluster. The framework works in such a manner that it is capable enough to provide distributed storage and processing over the same cluster. It is designed to work on cheaper systems commonly known as commodity hardware where each system offers its local storage and computation power.

Hadoop is capable of running various file systems and HDFS is just one single implementation that out of all those file systems. The Hadoop has a variety of file systems that can be implemented concretely. The Java abstract class org.apache.hadoop.fs.FileSystem represents a file system in Hadoop.

Filesystem	URI scheme	Java implementation (all under org.apache.hadoop)	Description
Local	file	fs.LocalFileSystem	The Hadoop Local filesystem is used for a locally connected disk with client-side checksumming. The local filesystem uses RawLocalFileSystem with no checksums.
HDFS	hdfs	hdfs.DistributedFileSystem	HDFS stands for Hadoop Distributed File System and it is drafted for working with MapReduce efficiently.
HFTP	hftp	hdfs.HftpFileSystem	The HFTP filesystem provides read-only access to HDFS over HTTP. There is no connection of HFTP with FTP.  This filesystem is commonly used with distcp to share data between HDFS clusters possessing different versions.
HSFTP	hsftp	hdfs.HsftpFileSystem	The HSFTP filesystem provides read-only access to HDFS over HTTPS. This file system also does not have any connection with FTP.
HAR	har	fs.HarFileSystem	The HAR file system is mainly used to reduce the memory usage of NameNode by registering files in Hadoop HDFS. This file system is layered on some other file system for archiving purposes.
KFS (Cloud-Store)	kfs	fs.kfs.KosmosFileSystem	cloud store or KFS(KosmosFileSystem) is a file system that is written in c++. It is very much similar to a distributed file system like HDFS and GFS(Google File System).
FTP	ftp	fs.ftp.FTPFileSystem	The FTP filesystem is supported by the FTP server.
S3 (native)	s3n	fs.s3native.NativeS3FileSystem	This file system is backed by AmazonS3.
S3 (block-based)	s3	fs.s3.S3FileSystem	S3 (block-based) file system which is supported by Amazon s3 stores files in blocks(similar to HDFS) just to overcome S3’s file system 5 GB file size limit.

Hadoop gives numerous interfaces to its various filesystems, and it for the most part utilizes the URI plan to pick the right filesystem example to speak with. You can use any of this filesystem for working with MapReduce while processing very large datasets but distributed file systems with data locality features are preferable like HDFS and KFS(KosmosFileSystem).