Network file systems NFS in Operating System

Network file systems are commonplace. They are typically integrated with the overall directory structure and interface of the client system. NFS is a good example of a widely used, well implemented client–server network file system NFS is both an implementation and a specification of a software system for accessing remote files across LANs (or even … Read more

Recovery in Operating System

A system crash can cause inconsistencies among on-disk file-system data structures, such as directory structures, free-block pointers, and free FCB pointers. Many file systems apply changes to these structures in place. A typical operation, such as creating a file, can involve many structural changes within the file system on the disk. Directory structures are modified, … Read more

Efficiency and Performance in Operating System

Efficiency The efficient use of disk space depends heavily on the disk-allocation and directory algorithms in use. For instance, UNIX inodes are preallocated on a volume. Even an empty disk has a percentage of its space lost to inodes. However, by preallocating the inodes and spreading them across the volume, we improve the file system’s … Read more

Free-Space Management in Operating System

Since disk space is limited, we need to reuse the space from deleted files for new files, if possible. (Write-once optical disks allow only one write to any given sector, and thus reuse is not physically possible.) To keep track of free disk space, the system maintains a free-space list. The free-space list records all … Read more

Allocation Methods in Operating System

Three major methods of allocating disk space are in wide use: contiguous, linked, and indexed. Each method has advantages and disadvantages. Although some systems support all three, it is more common for a system to use one method for all files within a file-system type Contiguous Allocation Contiguous allocation requires that each file occupy a … Read more

Directory Implementation in Operating System

The selection of directory-allocation and directory-management algorithms significantly affects the efficiency, performance, and reliability of the file system Linear List The simplest method of implementing a directory is to use a linear list of file names with pointers to the data blocks. This method is simple to program but time-consuming to execute. To create a … Read more

Virtual File Systems in Operating System

Data structures and procedures are used to isolate the basic system call functionality from the implementation details. Thus, the file-system implementation consists of three major layers. The first layer is the file-system interface, based on the open(), read(), write(), and close() calls and on file descriptors The second layer is called the virtual file system … Read more

File-System Structure in Operating System

Disks provide most of the secondary storage on which file systems are maintained. Two characteristics make them convenient for this purpose: A disk can be rewritten in place; it is possible to read a block from the disk, modify the block, and write it back into the same place A disk can access directly any … Read more

Protection in operating System

Reliability is generally provided by duplicate copies of files. Many computers have systems programs that automatically (or through computer-operator intervention) copy disk files to tape at regular intervals (once per day or week or month) to maintain a copy should a file system be accidentally destroyed. File systems can be damaged by hardware problems (such … Read more