If you don’t get the title, skip this post. Discussion below the fold.
There is a discussion going on regarding ext3 and ext4, the Linux file systems, in relation to the nature of the journaling process.
The ext3 file system was discovered to have a significant delay when writing to the disk to th cache. I believe this is writing the journaling information specifically. This means that journaling data, which is supposed to be there to fix everything when data is lost during a crash of some kind, would no be accurate. Normally, journaling is timed like a transaction. So, to simplify, this would happen (troll feel free to correct or modify this description):
Journal: I’m about to do X.
In the data part of the disk: X is carried out
Journal: I just checked, and it appears that I did X.
Thus, using the journaling information, not only can you tell what the hard disk using parts of the system did, but also what was intended, and what did nor did not work. This means that when a system comes back up from a crash, it is a trivial matter to make things right.
However, if the disk data writing/reading is not synced with the journaling, then the journaling system is not only useless but maybe worse than useless. And there were indications that this was happening with the ext3 system.
And by the way, it does not matter if the delay is with data or journaling. Neither is good.
It turns out that ext4 is worse. The cache writing delay with ext3 is seconds, but with ext4 it may be minutes.
But of course, it is all a bit more complex than that even. An update of the discussion and some interesting commentary can be found here on Linux Mag web site. Enjoy.