6 - Disk Storage, Basic File Structures, and Hashing...

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Disk Storage, Basic File Structures, and Hashing (Lecture Session-6) Chapter 13 Wed, Feb 03, 2010 1 DLPD, BITS-Pilani. Prepared by Dr.R. Gururaj, Asst.Professor of CS
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Wed, Feb 03, 2010 DLPD, BITS-Pilani. Prepared by Dr.R. Gururaj, Asst.Professor of CS 2 •Disk Storage Devices •Files of Records •Operations on Files •Unordered Files •Ordered Files •Hashed Files •Dynamic and Extendible Hashing Techniques •RAID Technology Contents
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Wed, Feb 03, 2010 DLPD, BITS-Pilani. Prepared by Dr.R. Gururaj, Asst.Professor of CS 3 Disk Storage Devices Preferred secondary storage device for high storage capacity and low cost. Data stored as magnetized areas on magnetic disk surfaces. A disk pack contains several magnetic disks connected to a rotating spindle. Disks are divided into concentric circular tracks on each disk surface . Track capacities vary typically from 4 to 50 Kbytes or more
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Wed, Feb 03, 2010 DLPD, BITS-Pilani. Prepared by Dr.R. Gururaj, Asst.Professor of CS 4 A track is divided into smaller blocks or sectors because it usually contains a large amount of information The division of a track into sectors is hard-coded on the disk surface and cannot be changed. One type of sector organization calls a portion of a track that subtends a fixed angle at the center as a sector. A track is divided into blocks . The block size B is fixed for each system. Typical block sizes range from B=512 bytes to B=4096 bytes. Whole blocks are transferred between disk and main memory for processing.
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Wed, Feb 03, 2010 DLPD, BITS-Pilani. Prepared by Dr.R. Gururaj, Asst.Professor of CS 5
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Wed, Feb 03, 2010 DLPD, BITS-Pilani. Prepared by Dr.R. Gururaj, Asst.Professor of CS 6 A read-write head moves to the track that contains the block to be transferred. Disk rotation moves the block under the read-write head for reading or writing. A physical disk block (hardware) address consists of: a cylinder number (imaginary collection of tracks of same radius from all recorded surfaces) the track number or surface number (within the cylinder) and block number (within track). Reading or writing a disk block is time consuming because of the seek time s and rotational delay (latency) rd . Double buffering can be used to speed up the transfer of contiguous disk blocks.
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Wed, Feb 03, 2010 DLPD, BITS-Pilani. Prepared by Dr.R. Gururaj, Asst.Professor of CS 7
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Wed, Feb 03, 2010 DLPD, BITS-Pilani. Prepared by Dr.R. Gururaj, Asst.Professor of CS 8 Records Fixed and variable length records Records contain fields which have values of a particular type E.g., amount, date, time, age Fields themselves may be fixed length or variable length Variable length fields can be mixed into one record: Separator characters or length fields are needed so that the record can be “parsed.”
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Wed, Feb 03, 2010 DLPD, BITS-Pilani. Prepared by Dr.R. Gururaj, Asst.Professor of CS 9 Blocking Blocking
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This note was uploaded on 03/14/2010 for the course CSE IS ZC332 taught by Professor Shailendrasshekhawat during the Summer '10 term at Birla Institute of Technology & Science.

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6 - Disk Storage, Basic File Structures, and Hashing...

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