Re: Is it possible to suggest the active MDS to move to a datacenter ?

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Thanks for your answer.

Le jeudi 29 mars 2018 à 13:51 -0700, Patrick Donnelly a écrit :
> On Thu, Mar 29, 2018 at 1:02 PM, Nicolas Huillard <nhuillard@dolomede
> .fr> wrote:
> > I manage my 2 datacenters with Pacemaker and Booth. One of them is
> > the
> > publicly-known one, thanks to Booth.
> > Whatever the "public datacenter", Ceph is a single storage cluster.
> > Since most of the cephfs traffic come from this "public
> > datacenter",
> > I'd like to suggest or force the active MDS to move to the same
> > datacenter, hoping to reduce trafic on the inter-datacenter link,
> > and
> > reduce cephfs metadata operations latency.
> > 
> > Is it possible for forcefully move the active MDS using external
> > triggers ?
> 
> No and it probably wouldn't be beneficial. The MDS still needs to
> talk
> to the metadata/data pools and increasing the latency between the MDS
> and the OSDs will probably do more harm.

It wasn't clear in my first post: OSDs are already split between both
DCs, so having the MDS on either side has the same effect on MDS-OSD
traffic. It appears that my current usage profile generates load on the
 MDS, but not that much on OSD-metadata.
The public DC is just the one of the two that Booth gives its ticket
to.

> One possibility for helping your situation is to put NFS-Ganesha in
> the public datacenter as a gateway to CephFS. This may help with your
> performance by (a) sharing a larger cache among multiple clients and
> (b) reducing capability conflicts between clients thereby resulting
> in
> less metadata traffic with the MDS. Be aware an HA solution doesn't
> yet exist for NFS-Ganesha+CephFS outside of Openstack Queens
> deployments.

I'll keep it stupid-simple then, just use the cephfs client, and
monitor the usage profile of things ;-)

-- 
Nicolas Huillard
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