File system

[Eitan Adler]

gjournal will replay all write attempts
> (metadata and data) before the failure, so you should be relatively
> sure that all writes are done correctly.

As I understand it journals work by writing to disk a log of all the
changes that have to be made - waits for confirmation that it wrote
the data - and then attempts to make those changes. If after the
confirmation there is a crash the log file is replayed.
Certain virtual machines will report to the OS that it wrote the data
to disk before it actually does so. In that case journaling doesn't
actually help as the log file is still not on some form of stable
storage.
--
Eitan Adler