benefits of journaling for soft RAID ?

[Benno Senoner]

>

Hello,

>
>
> I had journaling and buffer commit code, but not any filesystem
> personality stuff.  Current status is that 2.2 is out (yay!) and
> journaling is once again my top priority, and I've just started doing
> real testing of basic filesystem transactions (currently only for the
> simplest case --- chmod --- but most of the others are relatively easy
> to add once that works properly).

sorry for my ignorance,
can someone please explain what journaling precisely does,
(is this a sort of mechanism, which leaves the filesystem in a consistent
status,
even in case of disk write interruption, due of power loss or other causes  ?)

and the advantages / disadvantages ( makes filesystem slower ?),
especially in conjunction with software/hardware RAID.

thanks for the infos,

regards,
Benno.