Qnx4fs
From Wikipedia, the free encyclopedia
QNX4FS is an extent-based file system used by the QNX4 and QNX6 operating systems.
The file system remains consistent even after a power failure, but this is NOT achieved by 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. (Note: However, that data may be lost, no file systems can work around this in fact because the actual contents of the hard-disk's cache RAM will always get lost on a power failure.) This design has a considerable performance gain over journaling, by just bypassing that step.
Another notable property of this file system is that its actual metadata, like inode 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's, or historically Unix's) philosophy that "everything is a file."
