A directory is a file that contains entries with information about other files in the system, including the file name, type, size, owner, protection, usage count, times of creation and last modification, and list of disk blocks used. A file system organizes storage across partitions, with each partition containing a directory of its files. Partitions are known as minidisks in IBM systems and volumes in PCs and Macs. Each directory records information about all files in its partition.
Useful documents for engineering students of CSE, and specially for students of aryabhatta knowledge university, Bihar (A.K.U. Bihar). It covers following topics, File concept, access methods, directory structure
Hadoop is a well-known framework used for big data processing now-a-days. It implements MapReduce for processing and utilizes distributed file system known as Hadoop Distributed File System (HDFS) to store data. HDFS provides fault tolerant, distributed and scalable storage for big data so that MapReduce can easily perform jobs on this data. Knowledge and understanding of data storage over HDFS is very important for a researcher working on Hadoop for big data storage and processing optimization. The aim of this presentation is to describe the architecture and process flow of HDFS. This presentation highlights prominent features of this file system implemented by Hadoop to execute MapReduce jobs. Moreover the presentation provides the description of process flow for achieving the design objectives of HDFS. Future research directions to explore and improve HDFS performance are also elaborated on.
1. Definition
• A directory is a file which contains information
about other files in the system
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2. Contents of a Directory Entry
Directory Information about each file
Entry1 File name
File type
Entry2 File size
Owner
Entry3 Protection information
Usage count
Creation time
Entry4
Time of last modification
List of disk blocks used
Fig : A directory having an entry for each file
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3. File System Organization
• File systems on a computer system need organization
• Organization done in two parts
1. Partition file system
2. Create directory
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4. Minidisks and Volumes
Partitions are known as
• Minidisks in IBM world
• Volumes in PC and Macinthosh arenas
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5. File System Organization
1. Partition file system
• Each disk on a system contains at least one partition
• A partition is a low level structure
• Each partition contains files and directories
• A single disk can have multiple partitions
• Each partition is treated as a separate storage device
i..e. each partition is a virtual disk
• Some systems group different physical disks into a single
partition
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6. File System Organization
2. Create directory
• Each partition contains a directory
• A directory is also known as a device directory or volume
table of contents ( VTOC )
• The directory records information about all files on that
partition
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7. File System Organization
directory
Partition A
files
directory Disk 1
Partition B files
Fig : File system organization – Single disk – Multiple partitions
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8. File System Organization
Directory
Disk 2
Partition C Files
Disk 3
Fig : File System organization – Single Partition – Multiple Disks
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10. 1. In sequential access method
a) Records are accessed randomly
b) Every alternate record is accessed
c) Records are accessed one after the other
d) None of the above
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11. 2. Direct access is suitable for
a) Payroll application
b) Compilation of a source program file
c) Airline reservation
d) All of the above
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12. 3. An index file
a) Increases speed of accessing data
b) Decreases speed of accessing data
c) Occupies space in addition to data file
d) Both a & c
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13. 4. The access method to be used for processing student
results
a) Direct access
b) Indexed access
c) Sequential Access
d) None of the above
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14. 5. A directory is
a) A file
b) A storage device
c) A system program
d) None of the above
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15. 6. Each entry in a directory stores information such as
a) Name of the file
b) Size of the file
c) Location of the file
d) All of the above
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16. 7. Which of the following is not a directory operation
a) Deleting a file
b) Creating a file
c) Rename a file
d) None
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17. 8. The most common backup device is
a) Keyboard
b) Printer
c) Magnetic tape
d) All of the above
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