Re: [Qemu-devel] [RFC V8 01/24] qcow2: Add journal specification.

[Stefan Hajnoczi]

On Wed, Jul 03, 2013 at 02:53:27PM +0200, Benoît Canet wrote:
> > By the way, I don't know much about journalling techniques.  So I'm
> > asking you these questions so that either you can answer them straight
> > away or because they might warrant a look at existing journal
> > implementations like:
> 
> I tried to so something simple and performing for the deduplication usage.
> 
> That explain that there is no concept of transaction and that the journal's
> block are flushed asynchronously in order to have an high insertion rate.
> 
> I agree with your previous comment is more a log than a journal.

Simple is good.  Even for deduplication alone, I think data integrity is
critical - otherwise we risk stale dedup metadata pointing to clusters
that are unallocated or do not contain the right data.  So the journal
will probably need to follow techniques for commits/checksums.

Stefan