QNX4FS is an extent-based
file system used by the
QNX4 and QNX6 operating systems.
As the file system uses
soft updates
Soft updates is an approach to maintaining file system metadata integrity in the event of a crash or power outage. Soft updates work by tracking and enforcing dependencies among updates to file system metadata. Soft updates are an alternative t ...
, it remains consistent even after a
power failure
A power outage, also called a blackout, a power failure, a power blackout, a power loss, a power cut, or a power out is the complete loss of the electrical power network supply to an end user.
There are many causes of power failures in an el ...
, without using
journaling. Instead, the writes are carefully ordered and flushed to
disk at appropriate intervals so that the on-disk structure always remains consistent, no matter if the operation is interrupted. However, unflushed changes to the file system are nevertheless lost, as the
disk cache is typically stored in
volatile memory
Volatile memory, in contrast to non-volatile memory, is computer memory that requires power to maintain the stored information; it retains its contents while powered on but when the power is interrupted, the stored data is quickly lost.
Volatile ...
.
Another notable property of this file system is that its actual metadata, like
inode
An inode (index node) is a data structure in a Unix-style file system that describes a file-system object such as a file or a directory. Each inode stores the attributes and disk block locations of the object's data. File-system object attribu ...
information and disk bitmaps, are accessible in the same way as any other file on the file system (as
/.inodes and
/.bitmap, respectively).
This is consistent with QNX's (in fact,
Plan 9 from Bell Labs
Plan 9 from Bell Labs is a distributed operating system which originated from the Computing Science Research Center (CSRC) at Bell Labs in the mid-1980s and built on UNIX concepts first developed there in the late 1960s. Since 2000, Plan 9 has ...
's, or historically
Unix
Unix (, ; trademarked as UNIX) is a family of multitasking, multi-user computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, a ...
's) philosophy that "
everything is a file
"Everything is a file" is an approach to interface design in Unix derivatives.
While this turn of phrase does not as such figure as a Unix design principle or philosophy,
it is a common way to analyse designs, and informs the design of new interfa ...
".
References
External links
*
BlackBerry
Disk file systems
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