Berkeley COMPSCI 162 - Lecture 18 File Systems, Naming, and Directories (7 pages)

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Lecture 18 File Systems, Naming, and Directories



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Lecture 18 File Systems, Naming, and Directories

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Pages:
7
School:
University of California, Berkeley
Course:
Compsci 162 - Operating Systems and System Programming
Operating Systems and System Programming Documents

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Review Magnetic Disk Characteristic Cylinder all the tracks under the head at a given point on all surface Head Read write data is a three stage process CS162 Operating Systems and Systems Programming Lecture 18 Track Sector Cylinder Platter Seek time position the head arm over the proper track into proper cylinder Rotational latency wait for the desired sector to rotate under the read write head Transfer time transfer a block of bits sector under the read write head File Systems Naming and Directories Disk Latency Queueing Time Controller time Seek Time Rotation Time Xfer Time Media Time Seek Rot Xfer Result Software Queue Device Driver Hardware Controller Request April 7 2008 Prof Anthony D Joseph http inst eecs berkeley edu cs162 Highest Bandwidth transfer large group of blocks sequentially from one track 4 7 08 Review Multilevel Indexed Files UNIX 4 1 Multilevel Indexed Files Like multilevel address translation from UNIX 4 1 BSD Joseph CS162 UCB Spring 2008 Lec 18 2 Review Example of Multilevel Indexed Files Sample file in multilevel indexed format How many accesses for block 23 assume file header accessed on open Key idea efficient for small files but still allow big files Two One for indirect block one for data How about block 5 One One for data Block 340 File hdr contains 13 pointers Three double indirect block indirect block and data Fixed size table pointers not all equivalent This header is called an inode in UNIX UNIX 4 1 Pros and cons File Header format Pros Simple more or less Files can easily expand up to a point Small files particularly cheap and easy Cons Lots of seeks Very large files must read many indirect blocks four I Os per block First 10 pointers are to data blocks Ptr 11 points to indirect block containing 256 block ptrs Pointer 12 points to doubly indirect block containing 256 indirect block ptrs for total of 64K blocks Pointer 13 points to a triply indirect block 16M blocks 4 7 08 Joseph CS162 UCB Spring 2008 4 7 08 Lec 18 3 Page 1 Joseph



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