On Wed, Oct 12, 2016 at 2:45 AM, Frédéric Nass
<frederic.n...@univ-lorraine.fr> wrote:
> Can we use rbd journaling without using rbd mirroring in Jewel ?

Yes, you can use journaling without using rbd-mirroring, but ...

>So that we
> can set rbd journals on SSD pools and improve write IOPS on standard (no
> mirrored) RBD images.
> Assuming IOs are acknowleged when written to the journal pool.

... write ops are acked as soon as they are written to the in-memory
cache or, if disabled, when the backing image is updated. The journal
is not used to satisfy read-after-write requests, so we cannot ack a
write op until a read can safely (and consistently) be performed --
either from the in-memory cache or from the backing image.


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