The Design of HDFS

- Very large files
- Streaming data access (write one, read many times)
- Commodity hardware

Not good for those applications which:
+ Low-latency data access (need quick response time)
+ Lots of small files: information of file is stored in namenode. Each file, directory, and block takes about 150 bytes. So, for example, if you had one million files, each taking one block, you would need at least 300 MB of memory.
+ Multiple writers, arbitrary file modifications: There is no support for multiple writers or for modifications at arbitrary offsets in the file.