[ceph-users] New OSD with weight 0, rebalance still happen...

Matthew H matthew.heler at hotmail.com
Fri Nov 23 08:04:36 PST 2018


Greetings,

You need to set the following configuration option under [osd] in your ceph.conf file for your new OSDs.

[osd]
osd_crush_initial_weight = 0

This will ensure your new OSDs come up with a 0 crush weight, thus preventing the automatic rebalance that you see occuring.

Good luck,

________________________________
From: ceph-users <ceph-users-bounces at lists.ceph.com> on behalf of Marco Gaiarin <gaio at sv.lnf.it>
Sent: Thursday, November 22, 2018 3:22 AM
To: ceph-users at ceph.com
Subject: [ceph-users] New OSD with weight 0, rebalance still happen...


Ceph still surprise me, when i'm sure i've fully understood it,
something 'strange' (to my knowledge) happen.


I need to move out a server of my ceph hammer cluster (3 nodes, 4 OSD
per node), and for some reasons i cannot simply move disks.
So i've added a new node, and yesterday i've setup the new 4 OSD.
In my mind i will add 4 OSD with weight 0, and then slowly i will lower
the old OSD weight and increase the weight of the new.

I've done before:

        ceph osd set noin

and then added OSD, and (as expected) new OSD start with weight 0.

But, despite of the fact that weight is zero, rebalance happen, and
using percentage of rebalance 'weighted' to the size of new disk (eg,
i've had 18TB circa of space, i've added a 2TB disks and roughly 10% of
data start to rebalance).


Why? Thanks.

--
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