This is an PPT of Operating System. It include the following topic " File System Reliability & Virtual File in Operating System ".

1. TOPIC : FILE SYSTEM RELIABILITY & VIRTAUL FILE
SYSTEM
PRESENTED BY:
MEGHAJ KUMAR MALLICK
(MCA/25017/18)
1ST YEAR ,2ND SEMESTER

3.  What can happen if disk loses power or
machine software crashes?
◦ Some operations in progress may complete
◦ Some operations in progress may be lost
◦ Overwrite of a block may only partially complete
 File system wants durability (as a minimum!)
◦ Data previously stored can be retrieved (maybe
after some recovery step), regardless of failure

4.  Single logical file operation can involve
updates to multiple physical disk blocks
◦ inode, indirect block, data block, bitmap, …
◦ With remapping, single update to physical disk
block can require multiple (even lower level)
updates
 At a physical level, operations complete one
at a time
◦ Want concurrent operations for performance
 How do we guarantee consistency regardless
of when crash occurs

5.  Volatile storage – information stored here
does not survive system crashes
◦ Example: main memory, cache
 Nonvolatile storage – Information usually
survives crashes
◦ Example: disk and tape
 Stable storage – Information never lost
◦ Not actually possible, so approximated via
replication or RAID to devices with independent
failure modes

6.  Sequence operations in a specific order
◦ Careful design to allow sequence to be interrupted
safely
 Post-crash recovery
◦ Read data structures to see if there were any
operations in progress
◦ Clean up/finish as needed
 Approach taken in FAT, FFS (fsck), and many
app-level recovery schemes (e.g., Word)

8.  A virtual file system (VFS) is programming that forms an
interface between an operating system's kernel and a
more concrete file system.
 The VFS serves as an abstraction layer that gives
applications access to different types of file systems
and local and network storage devices. For that reason,
a VFS may also be known as a virtual file system switch.
It also manages the data storage and retrieval between
the operating system and the storage sub-system. The
VFS maintains a cache of directory lookups to enable
easy location of frequently accessed directories.

9.  One of the first virtual file system
mechanisms on Unix-like systems was
introduced by Sun Microsystemsin SunOS 2.0
in 1985
 In Microsoft Windows, virtual file systems can
also be implemented through userland Shell
namespace extensions.

10.  Sometimes Virtual File System refers to a file
or a group of files (not necessarily inside a
concrete file system) that acts as a
manageable container which should provide
the functionality of a concrete file system
through the usage of software.

11.  Examples of such containers are CBFS
Storage or a single-file virtual file system in
an emulator like PCTask or so-called WinUAE,
Oracle's VirtualBox, Microsoft's Virtual
PC, VMware.
 The primary benefit for this type of file
system is that it is centralized and easy to
remove

12.  Direct examples of single-file virtual file
systems include emulators, such as PCTask
and WinUAE, which encapsulate not only the
file system data but also emulated disk
layout. This makes it easy to treat an OS
installation like any other piece of software—
transferring it with removable media or over
the network.