The Hadoop Distributed File System (HDFS) is a distributed, scalable, and portable file system written in Java for the Hadoop framework. It provides high-throughput access to application data, and similar functionality to that provided by the Google File System.
HDFS is highly fault-tolerant and is designed to be deployed on low-cost hardware. HDFS is suitable for applications that have large data sets. HDFS relaxes a few POSIX requirements to enable streaming access to file system data.
Each node in a Hadoop instance typically has a single namenode; a cluster of datanodes form the HDFS cluster. The situation is typical because each node does not require a datanode to be present. Each datanode serves up blocks of data over the network using a block protocol specific to HDFS.
HDFS is designed to scale to tens of petabytes of storage and runs on top of the filesystems of the underlying operating systems. It is a sub-project of the Apache Hadoop project.
Features include:
- Supports very large files.
- Master/slave architecture.
- Simple Coherency Model.
- Data access via MapReduce streaming.
- Easily portable from one platform to another.
- Supports a traditional hierarchical file organization.
- Designed to reliably store very large files across machines in a large cluster. It stores each file as a sequence of blocks; all blocks in a file except the last block are the same size.
- Blocks of a file are replicated for fault tolerance across multiple hosts, avoiding the need for RAID storage.
- Safemode.
- Persistence of File System Metadata.
- HDFS communication protocols are layered on top of the TCP/IP protocol.
- Compatible with data rebalancing schemes.
- Checksum checking on the contents of HDFS files.
- Snapshots.
Website: hadoop.apache.org
Support: Users Guide
Developer: The Apache Software Foundation
License: Apache License 2.0
HDFS is written in Java. Learn Java with our recommended free books and free tutorials.
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