File System Mounting

File System Mounting

• Files contained in a file system can be accessed only when the file system is mounted. Each device consists of its own local file system. Mounting is the operation that administrator/user perform to cause the file system on a physical storage device to appear as part of the file system.

• Mount system call is used on UNIX/Linux OS for mounting file system and unmount system call for disconnecting the file system. Mounting file system is used when there are more than one file system is used. Required file system is mounted in the host file system machine as a root directory.

• Some operating system support the mounting the file system at any point.

• File system stores directories and files. Each file system contains exactly one directory at the very top level, called the root directory for that file system. This root directory can contain other directories and files. One file system is designated the root file system or /. Every other file system is mounted under the root file system.

Procedure for mounting file system :

• To mount the file system, device name and location within the file structure

• Fig. 6.4.1 shows the mounting a file system on secondary storage device. File system manage mounted directories by using mount table. User can create soft links to files in mounted file system. Mount tables keep track of the actual physical location of the files.

• When a file system is mounted, the client can reference files by the local path name. There is no reference to remote host location, although files remain physically located at the remote site.

Busy file system is can not unmount by using unmount command. A file system is considered busy in following situation :

1. File system is shared in between the users.

2. A program has a file open in that file system.

3. A user is accessing a file/directory in the file system.

Example: Consider a file structure of the pen drive. Following is Fig. 6.4.2 of file

• The file system structure in the pen drive is as follows:

• Now, the pen drive is mounted to the directory sorting_program. Here, the pen drive becomes the part of the file

Advantages of mounting:

1. It is a user-oriented naming scheme

2. It makes sense to be able to mount at any level.

Disadvantages of mounting :

1. The hardware is less obvious since devices can be located anywhere in the tree structure

Example 6.4.1 Discuss the advantages and disadvantages of supporting links to files that cross mount points.

Solution :

Advantages:

1. Greater transparency

2. User does not need to be aware of mount points.

Disadvantages:

1. The error condition would expose to the user that a link is a dead link and that the link does indeed cross file system boundaries.