What is Journaling

A journaling file system is more reliable when it comes to data storage. Journaling file systems do not necessarily prevent corruption, but they do prevent inconsistency and are much faster at file system checks than non-journaled file systems. If a power failure happens while you are saving a file, the save will not complete and you end up with corrupted data and an inconsistent file system. Instead of actually writing directly to the part of the disk where the file is stored, a journaling file system first writes it to another part of the hard drive and notes the necessary changes to a log, then in the background it goes through each entry to the journal and begins to complete the task, and when the task is complete, it checks it off on the list. Thus the file system is always in a consistent state (the file got saved, the journal reports it as not completely saved, or the journal is inconsistent (but can be rebuilt from the file system)). Some journaling file systems can prevent corruption as well by writing data twice.

in Unix file systems, files are indexed by a number, called the inode, and each inode has several attributes associated with it, like permissions, name, etc. When you delete a file, what really happens is the inode is unlinked from the filename, but if some other program is using the file, it still has a link open to the OS, and will continue to be updated. A file is not really deleted until all links have been removed (even then, the data is still on the disk, but not indexed in anyway and thus very hard to recover). All of this means that you can delete executing programs while they’re running without crashing and move files before they’re finished downloading without corruption.


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