Amish K. Munshi wrote: > I wanted to know what is journaling file system and how does it > differ from the previous file systems.
Amish, I'm a newbie too, but I'm going to try to answer your question so I can learn when somebody corrects me. (Based on other knowledge I think I have (of journaling in a database), ;-) a journaling file system keeps a record of the changes that have been made to the filesystem, complete with enough information to reconstruct them. (This is in addition to actually making the changes on the disk, or maybe this is until the changes are written from cache to the disk?) If anything occurs to indicate that there might be a problem (like an unexpected shutdown), the filesystem can be reconstructed from the journal entries. Thus, for example, if your computer goes down due to a power failure, instead of going through the fsck process, the journaling file system reviews its journal entries and reconstructs anything (that hasn't yet made it to the disk yet? -- see below). This process is much faster and more reliable than the fsck process. I glossed over some things above, so state the following as specific things I'm not sure about: * How does the journaling file system manage itself? (Perhaps it keeps the journal only for file system operations that might be in cache, and deletes those entries when that part of the cache is written to disk??) * Hmm, maybe if I know the answer to the previous item it answers most of my questions. > Also is ext3 also a journaling file system? Yes. Also, I understand it is very compatible with ext2, you can change one to the other without too much trouble. Civleme (and others?) has posted good information comparing several of the journaling file systems for speed, reliability (maturity?), and so forth. Randy Kramer PS: I understand that the fsck process cannot always repair an ext2 filesystem after a power outage (unless you use "repair" in the Microsoft sense -- (IIUC) deleting a damaged file). I've switched to a journaling file system (jfs) in hopes that my data is much more secure.
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