As we all know, Operating Systems treat disks as objects that can be trusted not to change state without any activity prompt. When reading or writing files, OSs expect the files to remain accessible and not suddenly disappear in mid-read or mid-write process.

When a file is open, a program reading the file expects to be able to return to it and continue reading. Similarly, write commands may be dispatched to a writing subroutine and forgotten by the main program, so if a drive disappears between the time the subroutine is called and the data is written to disk, that data is lost forever.

Long before the advancement of technology like we have today, there were formal processes to physically “mount” and “unmount” storage media, and the physical act of mounting a tape or a disk triggered some mechanical switch to detect the presence or absence of media. Once the mechanism was engaged, the software could start to use the media (a “soft mount”). Some media even had mechanical interlock to prevent media from being ejected or removed until the software finished processing, and then using the media released the lock.

The Macintosh floppy and optical disk provide more modern examples of an interlocked physical and soft mount. One could only eject media through a software command, but that command might fail if some program was holding a file open on the medium. Enter USB connected storage. There is no mechanical interlock in a USB connection to coordinate the hard and soft mount. The user can decide to rip the disk out of the system at any time, and endure all manner of programs freaking out about the sudden loss of media.

Though there are implications of ripping a disk pack out of an operating system without a prompt command. These effects range from; Lost of data, to corrupted files, crashing programs, hanging computers requiring a reboot etc. A safe removal executes the “soft unmount” needed to prevent any unexpected Bad Things that may happen if a program loses its access to media.

Whereas, a due process or safe removal, does the following;

1. It flushes all active writes to disk.

2. It alerts all programs that are built to be alerted, that the disk is exiting, prompting them to take appropriate action.

3. Lets the user know when programs fail to take action, due to certain mechanical, programme malfunction etc and still are holding files open.

A disk can always be removed at any time we choose to, but that action leaves us at the mercy of how well, programs using the disk, cope with the sudden disappearance of that disk.

In the modern computer, many steps have been taken to defend against the careless removal of media. For instance, Windows has a feature called “Optimize for Quick Removal” which makes sure data is written quickly, instead of written in batches since it's difficult to get people to change habits.



Culled From; http://www.naijareporters.com/2015/07/the-effects-of-careless-storage-media.html?m=1

Nice write up.