1 Pertemuan 22 Implementasi Sistem File Matakuliah: T0316/sistem Operasi Tahun: 2005 Versi/Revisi:...
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Transcript of 1 Pertemuan 22 Implementasi Sistem File Matakuliah: T0316/sistem Operasi Tahun: 2005 Versi/Revisi:...
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Pertemuan 22Implementasi Sistem File
Matakuliah : T0316/sistem Operasi
Tahun : 2005
Versi/Revisi : 5
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Learning Outcomes
Pada akhir pertemuan ini, diharapkan mahasiswa
akan mampu :• menunjukkan implementasi sistem file (C3)
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Outline Materi
• Contiguous Allocation• Linked list allocation• Linked list allocation using Table• I-Nodes• Implementasi directory• Disk space management
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File System Implementation
A possible file system layout
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Implementing Files (1)
(a) Contiguous allocation of disk space for 7 files
(b) State of the disk after files D and E have been removed
+ simplicity: only remember disk address & number of blocks in the file
read performance
– fragmentation
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Implementing Files (2)
Storing a file as a linked list of disk blocks
+ minimal fragmentation
– random access is slow
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Implementing Files (3)
Linked list allocation using a file allocation table (FAT) in RAM
+ minimal fragmentation, random access is easier
– entire table must be in memory all the time
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Implementing Files (4)
An example i-node
+ in memory when the file is open
– disk address may insufficient use the last address as the address of more disk block addresses
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Implementing Directories
The directory entries provide information needed to find the disk blocks
The information may be:
• the disk address of the entire file (contiguous)
• the number of first block (linked list)
•The number of I-node
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Implementing Directories (1)
(a) A simple directory (for MS-DOS/Windows)fixed size entries
disk addresses and attributes in directory entry
(b) Directory in which each entry just refers to an i-node (for UNIX)
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Implementing Directories (2)
• Two ways of handling long file names in directory– (a) In-line– (b) In a heap
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Shared Files (1)
File system containing a shared file
– consistency problem in update
disk blocks are listed in the data structure/I-node instead of directories
OR
use symbolic linking which contains the file’s path name
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Shared Files (2)
(a) Situation prior to linking
(b) After the link is created
(c)After the original owner removes the file
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Disk Space Management (1)
• Dark line (left hand scale) gives data rate of a disk• Dotted line (right hand scale) gives disk space efficiency• All files 2KB
Block size
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Disk Space Management (2)
(a) Storing the free list on a linked list(b) A bit map
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Disk Space Management (3)
Quotas for keeping track of each user’s disk use
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File System Reliability
• Backups
• Strategies for dumping disk to a tape– Physical dump
• From block 0 until last
– Logical dump• Dump all files and directories changed since given
base date
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File System Reliability (1)-- Logical dump
• A file system to be dumped– squares are directories, circles are files– shaded items, modified since last dump– each directory & file labeled by i-node number
File that hasnot changed
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File System Reliability (2)
Bit maps used by the logical dumping algorithm(a) Dump changed files and all directories, then
(b) Dump changed files and directories above them(c) + (d) (b)
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File System Reliability (3)
• File system states(a) consistent(b) missing block(c) duplicate block in free list(d) duplicate data block
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File System Performance (1)
The block cache data structures
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File System Performance (2)
• I-nodes placed at the start of the disk• Disk divided into cylinder groups
– each with its own blocks and i-nodes
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Log-Structured File Systems
• With CPUs faster, memory larger– disk caches can also be larger– increasing number of read requests can come from
cache– thus, most disk accesses will be writes
• LFS Strategy structures entire disk as a log– have all writes initially buffered in memory– periodically write these to the end of the disk log– when file opened, locate i-node, then find blocks