What's It Mean By File System?

A file system is a data structure built inside a contiguous disk address space. A file
manager (FM) is a software package that manipulates file systems, but it is sometimes
called the file system. All operating systems have file managers. The primary task of a
file manager is to allocate and deallocate disk space into files within a file system.
A file system allows the disk space to be allocated to a large number of files. Each file
is made to appear as a contiguous address space to applications such as Oracle
Database. The files may not actually be contiguous within the disk space of the file
system. Files can be created, read, written, resized, and deleted. Each file has a name
associated with it that is used to refer to the file.
A file system is commonly built on top of a logical volume constructed by an LVM.
Thus all the files in a particular file system have the same performance, reliability, and
availability characteristics inherited from the underlying logical volume. A file system is a single pool of storage that is shared by all the files in the file system. If a file system
is out of space, then none of the files in that file system can grow. Space available in
one file system does not affect space in another file system. However some LVM/FM
combinations allow space to be added or removed from a file system.
An operating system can support multiple file systems. Multiple file systems are
constructed to give different storage characteristics to different files as well as to divide
the available disk space into pools that do not affect each other.