[Lustre-discuss] advice on OST journals in OSS failover pairs

[David Dillow]

On Mon, 2011-02-14 at 09:46 -0600, Cory Spitz wrote:
> You will find that async jounral commits don't help O_DIRECT I/O though.
>  So, maybe you should think about using both.

It definitely depends on your workload.

It's not in the paper at
http://www.usenix.org/events/fast10/tech/full_papers/oral.pdf

but I seem to recall that using external journals in conjunction with
async commits reduced the performance benefits from the async commits.
There does seem to be some bottlenecks with the external journalling
code paths, but since async worked so well for our workloads, we never
tried to run them down.

-- 
Dave Dillow
National Center for Computational Science
Oak Ridge National Laboratory
(865) 241-6602 office