1. DFS
Distributed File
System

2. Share Files Easily in
Public Folder

3. What about this type of networks?

4. What Is DFS In Real World?
DFS allows administrators to consolidate file
shares that may exist on multiple servers to
appear as though they all live in the same
location so that users can access them from a
single point on the network

5. Example:

6. Benefits of DFS
•
Resources management
– (users access all resources through a single point)
• Accessibility
– (users do not need to know the physical location of the shared folder,
then can navigate to it through Explorer and domain tree)
• Fault tolerance
– (shares can be replicated, so if the server in Chicago goes down,
resources still will be available to users)
• Work load management
– (DFS allows administrators to distribute shared folders and workloads
across several servers for more efficient network and server resources
use)

7. Hadoop

8. Assumptions and Goals (1)
• HDFS instance consist of thousands of server
• HDFS is always non-fuctional
• Automatic recovery is a architectural goals of
HDFS

9. Assumptions and Goals (2)
• HDFS needs streaming access to their DataSets
• HDFS is designed for batch processing rather
than interactive use y users
• HDFS has Large DataSets same as GB & TB

10. Assumptions and Goals (3)
• Moving Computation is Cheaper Than Moving
Data
• Portability across Heterogenous HW & SW

11. NameNode and DataNodes (1)
• Master/slave architecture
• An HDFS cluster consists of:
- Single NameNode
- a Master Server
manages file system namespace and regulates access to files by clients
- Number of DataNodes
One per node in cluster
Manage storage attached to the nodes they run on

12. NameNode and DataNodes (2)
• Internally, a file is split into one or more
blocks and these blocks are stored in a set of
DataNodes
• The NameNode executes file system
namespace operations like opening, closing,
and renaming files and directories

13. NameNode and DataNodes (3)
• The DataNodes are responsible for serving
read and write requests from the file system’s
clients
• The DataNodes also perform block creation,
deletion, and replication upon instruction
from the NameNode

14. NameNode and DataNodes (4)

15. NameNode and DataNodes (5)
• HDFS Run a GNU/Linux operating system (OS)
• HDFS is built using the Java language

16. File System NameSpace (1)
• HDFS supports a traditional hierarchical file
organization
• HDFS does not yet implement user access
permissions
• HDFS does not support hard links or soft links
• NameNode maintains the file system namespace

17. File System NameSpace (2)
• An application can specify the number of
replicas of a file that should be maintained by
HDFS
• The number of copies of a file is called the
replication factor of that file

18. Data Replication (1)
• HDFS reliably store very large files across
machines in a large cluster.
• It stores each file as a sequence of blocks
• all blocks except the last block are same size
• The block size and replication factor are
configurable per file

19. Data Replication (2)
• NameNode makes all decisions for replication
of blocks.
• It periodically receives a Heartbeat and a
Blockreport from each of DataNodes in the
cluster

20. Data Replication (3)
• Receipt of a Heartbeat implies that the
DataNode is functioning properly.
• A Blockreport contains a list of all blocks on a
DataNode

21. Data Replication (4)

22. File System Metadata (1)

23. File System Metadata (2)
• EditLog
– records any changes in File system
• FSimage
– Stores blockmaping and filesystem properties

24. File System Metadata (3)
• The NameNode keeps an image of the entire file
system namespace and file Blockmap in memory.
• This key metadata is compact, (4GB of RAM = huge
number of files)
• checkpoint
– NN starts up, it reads the FsImage and EditLog
– applies all the transactions from the EditLog to the in-
memory representation of the FsImage
– flushes out this new version into a new FsImage on disk.
– checkpoint only occurs when the NameNode starts up.

25. • Blockreport
– When a DataNode starts up, it scans through its
local file system, generates a list of all HDFS data
blocks that correspond to each of these local files
and sends this report to the NameNode

26. Robustness
• Cluster Rebalancing
• Data Integrity(checksum)
• Metadata Disk Failure
• Snapshots

27. Refrences:
1. http://www.maxi-pedia.com/what+is+DFS
2. www.Apachi.org