File Systems - Applied Operating System - Lecture Slides, Slides of Computer Science

Download File Systems - Applied Operating System - Lecture Slides and more Slides Computer Science in PDF only on Docsity! File Systems Chapter 6 6.1 Files 6.2 Directories 6.3 File system implementation 6.4 Example file systems Docsity.com Long-term Information Storage 1. Must store large amounts of data 2. Information stored must survive the termination of the process using it 3. Multiple processes must be able to access the information concurrently Docsity.com File Access • Sequential access – read all bytes/records from the beginning – cannot jump around, could rewind or back up – convenient when medium was mag tape • Random access – bytes/records read in any order – essential for data base systems – read can be … • move file marker (seek), then read or … • read and then move file marker Docsity.com File Operations 1. Create 2. Delete 3. Open 4. Close 5. Read 6. Write 7. Append 8. Seek 9. Get attributes 10.Set Attributes 11.Rename Docsity.com Memory-Mapped Files (a) Segmented process before mapping files into its address space (b) Process after mapping existing file abc into one segment creating new segment for xyz Docsity.com Hierarchical Directory Systems A hierarchical directory system Docsity.com Directory Operations 1. Create 2. Delete 3. Opendir 4. Closedir 5. Readdir 6. Rename 7. Link 8. Unlink Docsity.com 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 Docsity.com Implementing Directories (2) • Two ways of handling long file names in directory – (a) In-line – (b) In a heap Docsity.com Shared Files (2) (a) Situation prior to linking (b) After the link is created (c)After the original owner removes the file Docsity.com Disk Space Management (2) (a) Storing the free list on a linked list (b) A bit map Docsity.com File System Reliability (3) • File system states (a) consistent (b) missing block (c) duplicate block in free list (d) duplicate data block Docsity.com File System Performance (1) The block cache data structures Docsity.com 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 Docsity.com The MS-DOS File System (2) • Maximum partition for different block sizes • The empty boxes represent forbidden combinations Docsity.com The Windows 98 File System (1) The extended MOS-DOS directory entry used in Windows 98 Bytes Docsity.com The Windows 98 File System (2) An entry for (part of) a long file name in Windows 98 Bytes Checksum Docsity.com