Podcast
Questions and Answers
What is the primary role of the Name Node in HDFS?
What is the primary role of the Name Node in HDFS?
- To handle client requests for data processing
- To ensure data replication across nodes
- To store all the data blocks in the cluster
- To manage metadata and direct data block locations (correct)
What happens when a data node fails during write operations in HDFS?
What happens when a data node fails during write operations in HDFS?
- The client is notified to find alternative nodes
- The missing blocks are identified and replicated by the Name Node (correct)
- The Name Node allocates storage on a new data node instantly
- The write operation fails and must be retried
What is the Secondary Name Node's main purpose in HDFS?
What is the Secondary Name Node's main purpose in HDFS?
- To help manage metadata and periodically merge file system images (correct)
- To serve as a backup for data storage
- To operate the web-based interface for Hadoop
- To directly handle read and write operations from clients
In HDFS write operations, where are the replicas typically stored to optimize reliability and bandwidth?
In HDFS write operations, where are the replicas typically stored to optimize reliability and bandwidth?
What is one of the main trade-offs to consider when determining how to replicate data in HDFS?
What is one of the main trade-offs to consider when determining how to replicate data in HDFS?
What is the primary role of a Data Node in HDFS?
What is the primary role of a Data Node in HDFS?
What is the main function of the Name Node in HDFS?
What is the main function of the Name Node in HDFS?
What is the purpose of the Secondary Name Node in HDFS?
What is the purpose of the Secondary Name Node in HDFS?
During an HDFS read operation, which component is primarily responsible for serving the requested data?
During an HDFS read operation, which component is primarily responsible for serving the requested data?
Which statement best describes how HDFS handles data replication?
Which statement best describes how HDFS handles data replication?
What potential issue does HDFS overcome by utilizing a Master-Slave architecture?
What potential issue does HDFS overcome by utilizing a Master-Slave architecture?
How does HDFS ensure efficient organization of data across distributed nodes?
How does HDFS ensure efficient organization of data across distributed nodes?
Which of the following statements is NOT true about HDFS write operations?
Which of the following statements is NOT true about HDFS write operations?
Which of the following describes the functionality of the Name Node?
Which of the following describes the functionality of the Name Node?
Why does HDFS allow clients to read blocks directly from Data Nodes instead of going through the Name Node?
Why does HDFS allow clients to read blocks directly from Data Nodes instead of going through the Name Node?
How does HDFS determine which replica of a block a client should read?
How does HDFS determine which replica of a block a client should read?
What mechanism does HDFS use to ensure Data Nodes are operational?
What mechanism does HDFS use to ensure Data Nodes are operational?
What role does the edit log play in HDFS?
What role does the edit log play in HDFS?
What occurs if the Name Node does not hear from a Data Node within 10 minutes?
What occurs if the Name Node does not hear from a Data Node within 10 minutes?
Flashcards
HDFS Write Process
HDFS Write Process
Client contacts the NameNode, which directs the client to specific DataNodes for writing data blocks. The client writes data directly to the DataNodes, ensuring the specified replication factor. The NameNode handles potential failures by replicating missing blocks.
HDFS Replication Strategy
HDFS Replication Strategy
HDFS replicates data blocks to improve reliability. Strategies may involve placing replicas on a single node, different racks, or a blend, trading-off read/write bandwidth versus reliability.
HDFS Interface
HDFS Interface
HDFS offers methods for interacting with the file system, including a web-based interface and a command-line interface (Hadoop FS Shell).
NameNode
NameNode
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DataNodes
DataNodes
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HDFS
HDFS
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Commodity Hardware
Commodity Hardware
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Master-Slave Architecture
Master-Slave Architecture
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Rack
Rack
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Replication
Replication
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Secondary Name Node
Secondary Name Node
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HDFS Name Node
HDFS Name Node
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HDFS Replication
HDFS Replication
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HDFS Read Process
HDFS Read Process
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Data Block Replication
Data Block Replication
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Name Node Failure Handling
Name Node Failure Handling
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Heartbeating
Heartbeating
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Client-NN interaction in read
Client-NN interaction in read
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Study Notes
HDFS Overview
-
HDFS stands for Hadoop Distributed File System
-
Motivation for HDFS comes from the following problems:
- Data too large for a single machine
- Expensive high-end machines
- Commodity hardware failure
- Data loss if a storing machine fails
- Distributed machines need a coordinated way to organize data
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HDFS solves these issues via:
- Storing data on multiple machines
- Running on commodity hardware
- Software handling hardware failure
- Replicating data
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Commodity hardware is readily available, inexpensive, and interchangeable
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HDFS uses a Master-Slave architecture
- Master node (Name Node) controls file system
- Manages file system name space
- Manages block mappings
- Slave nodes (Data Nodes) are workhorses
- Perform block operations
- Handle replication
- Master node (Name Node) controls file system
-
Rack awareness policies are used to improve performance
- No more than one replica on one node
- No more than two replicas on the same rack
- For a replication factor of 3
- First replica on the local rack, second replica on different node in the same rack, third replica on a different rack
HDFS Inside
- Name Node handles snapshots of file system, edit logs, replication factors and block IDs
- Name Node periodically sends control information to Data Nodes
- Data Nodes are periodically checked by Name Node -if Name Node does not hear from a Data Node within 10 minutes it starts replicating the associated blocks
HDFS Inside: Read
- Clients connect directly to Data Nodes to read data
- Name Node gives directions on where to find data
- Clients read data from Data Nodes, bypassing Name Node
- if Data Nodes fail, client can connect to another Data node to get the missing block
HDFS Inside: Read-Reasons
- Prevents Name Node from being a bottleneck
- Allows HDFS to handle many concurrent clients
- Spreads data traffic across the cluster
HDFS Inside: Read-Replica Selection
- Name Node uses rack awareness to select replicas based on network topology
HDFS Inside: Write
- Clients connect to Name Node to write data
- Name Node directs clients to Data Nodes
- Clients write blocks to Data Nodes using the desired replication factor
- Name Node handles replication if a Data Node fails
HDFS Inside: Write-Replication Strategy
- Different replication strategies have tradeoffs in reliability, write bandwidth, and read bandwidth
- Putting all replicas on one node maximizes reliability but hurts write and read bandwidth
- Putting all replicas on different racks balances these factors
- HDFS replication strategies:
- 1 -> same node as client
- 2 -> different node in same rack
- 3 -> different node in different rack
HDFS Interface
- HDFS has a web based interface :
http://ccl.cse.nd.edu/operations/hadoop/ - Command Line Interface :
https://hadoop.apache.org/docs/r2.4.1/hadoop-project-dist/hadoop-common/FileSystemShell.html
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Description
This quiz covers the fundamentals of the Hadoop Distributed File System (HDFS). You will learn about its architecture, benefits, and how it addresses data storage challenges using commodity hardware. Gain insights into the Master-Slave structure, file management, and rack awareness policies.
