Journaling FS coming in 10.2.2!

K

kommakazi

Hack the Planet!@#
According to <a href=http://www.eweek.com/article2/0,3959,634711,00.asp>this</a> article, Apple is to include Journaling File System capability in 10.2.2. It will run on top of HFS+ and be turned off by default. Turning it on results in a 10-15% system performace hit, but this feature may still be useful for some. Guess their hiring of the creator of the BeOS file system has finally amounted to something.
 
That is awesome. Too bad it takes such a performance hit. I've wanted this ever since I first installed BeOS on a PC many many moons ago :)
 
Ok, this may sound stupid, as I know nothing about journaling file systems, but if using one causes a performance decrease, what is the point?
 
A journaled file system not only tells you when a file was modified... it can also recreate the file and restore it to a state before it was modified. You have an audit trail of who made what changes when. Pretty much a must for all multi-user file servers.

It has many other uses but those are the most pronounced.
 
Audit trail? Maybe, I haven't heard that before. The advantage I've seen touted for a JFS is that if the power is cut then your fs isn't corrupted.
 
Which is exactly what Rhino_G3 said, if not a little indirectly. Since it keeps track of changes to files and can restore them, it keeps the FS from getting corrupted by just restoring the files.
 
prevents file corruption by brain failure as well as power failure.

who hasn'y saved a file and gone "flark! i meant to save a copy, not hose the original"
 
Originally posted by scruffy
prevents file corruption by brain failure as well as power failure.

who hasn'y saved a file and gone "flark! i meant to save a copy, not hose the original"
Click to expand...

Exactly. That's why I love this feature so much. I guess I'll just have to buy a new computer now :D
 
so what?? You can revert your whole computer back to a previous state with JFS?

Isn't that world's of data? Like... if you have a 40 GB hard drive, and you used up 30 GB on it, and you want to revert 20 GB of files..... how is that possible, your hard drive isn't big enough to remember how the computer was before.....
 
Well, not knowing anything about it, I would think it wouldn't have to remember everything, only what has changed (which is probably a small fraction of what is there). and that data could be highly compressed, I would think. However, not knowing how it works, I couldn't really say.
 
This would be a journaling file system, not a versioning one, so it only remember the changes that have been made recently. Say you were writing a file. The journal would be marked that you are writing to the file and that its in progress. When you finish writing to the file, it would mark that the write was completed. Now if the power got pulled durring the write, when the machine starts up again, it just has to replay the log to find which files need to be examined to bring the fs back to a clean state, rather than the current, non-journaled, behavior, which is to search the whole disk looking for dirty files.

Now, if the JFS was a full JFS and not just a MetaData JFS (which I believe Elvis is), it would also record the actual bytes being written to the file to the journal, and if the plug was pulled mid write, you wouldn't lose any data, or get garbage at the end of your files. Most JFS's don't do this type of journaling though, as its expensive (in space and overhead), and on systems that have to deal with large files, its almost never done.
 
The implementation of JFS under 10.2.2 will be a makeshift one. Everyone knows it's coming to the Mac OS, and everybody seems a little surprised it's coming this early, and in a .X.x release. Apple seems to be trying to slip it in under the radar, giving them enough time to modify it and let it mature before making it the cornerstone feature it will be by the time 10.3 ships.
 
Journaling file systems are wonderful if you need to manage very large servers inexcess of 1TB but there is nothing wrong with the soft update system that currently runs as it will rebuild automatically on reboot to last file written.
 
I don't know if Elvis will be necessarily makeshift, softupdates on FreeBSD certainly isn't. Problem is that until it comes out and there are some KB articles on it, we won't really know how its being done.

I do commend apple on doing something akin to softupdates though, because it will allow us to easily turn it on with out reformatting.
 
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