[ceph-users] tunable question

Manuel Lausch manuel.lausch at 1und1.de
Mon Oct 2 00:41:41 PDT 2017


We have similar issues.
After upgradeing from hammer to jewel the tunable "choose leave stabel"
was introduces. If we activate it nearly all data will be moved. The
cluster has 2400 OSD on 40 nodes over two datacenters and is filled with
2,5 PB Data. 

We tried to enable it but the backfillingtraffic is to high to be
handled without impacting other services on the Network.

Do someone know if it is neccessary to enable this tunable? And could
it be a problem in the future if we want to upgrade to newer versions
wihout it enabled?

Manuel Lausch

Am Thu, 28 Sep 2017 10:29:58 +0200
schrieb Dan van der Ster <dan at vanderster.com>:

> Hi,
> How big is your cluster and what is your use case?
> For us, we'll likely never enable the recent tunables that need to
> remap *all* PGs -- it would simply be too disruptive for marginal
> benefit.
> Cheers, Dan
> On Thu, Sep 28, 2017 at 9:21 AM, mj <lists at merit.unu.edu> wrote:
> > Hi,
> >
> > We have completed the upgrade to jewel, and we set tunables to
> > hammer. Cluster again HEALTH_OK. :-)
> >
> > But now, we would like to proceed in the direction of luminous and
> > bluestore OSDs, and we would like to ask for some feedback first.
> >
> > From the jewel ceph docs on tubables: "Changing tunable to
> > "optimal" on an existing cluster will result in a very large amount
> > of data movement as almost every PG mapping is likely to change."
> >
> > Given the above, and the fact that we would like to proceed to
> > luminous/bluestore in the not too far away future: What is cleverer:
> >
> > 1 - keep the cluster at tunable hammer now, upgrade to luminous in
> > a little while, change OSDs to bluestore, and then set tunables to
> > optimal
> >
> > or
> >
> > 2 - set tunable to optimal now, take the impact of "almost all PG
> > remapping", and when that is finished, upgrade to luminous,
> > bluestore etc.
> >
> > Which route is the preferred one?
> >
> > Or is there a third (or fourth?) option..? :-)
> >
> > MJ
> > _______________________________________________
> > ceph-users mailing list
> > ceph-users at lists.ceph.com
> > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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Manuel Lausch

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