On Tue, Dec 30, 2008 at 09:55:57AM +0300, Alex Tomas wrote:

one good thing about JBD is that you can't update target block and csum
atomically. so, either you use some form of COW or you use journalling.
given we already have JBD it'd make sense to use it?

I'm sorry, but I'm not following. Is that first sentence right?

The main disadvantage I see of using jbd at the moment is that I loose
the possibility of having checksums and data in a different device.

The only alternative to jbd that I have at the moment is the "two
metadatas" approach I explained in another email (but please let me know
if it wasn't clear).

They both provide what I need (atomicity in data and csum writes), one
is easier, more tested, but prevents a feature. The other is a bit more
difficult, untested and written my me, but allows a feature. I have no
idea, performance-wise, how they will behave (it is expected they suck,
according to the other emails).

At this moment I'm going with the two metadatas approach, because I
think it has less limitations and it'd be fun to write. If then it's
unfit for some reason, I can always go back and use jbd. But I'm
obviously open to suggestions and more alternatives.

Thanks a lot,
		Alberto