[ceph-users] How balancer module balance data

[bryansoong21]

Hello,

We are running a pacific 16.2.10 cluster and enabled the balancer module, here 
is the configuration:

[root@ceph-1 ~]# ceph balancer status
{
"active": true,
"last_optimize_duration": "0:00:00.052548",
"last_optimize_started": "Fri Nov 17 17:09:57 2023",
"mode": "upmap",
"optimize_result": "Unable to find further optimization, or pool(s) pg_num 
is decreasing, or distribution is already perfect",
"plans": []
}
[root@ceph-1 ~]# ceph balancer eval
current cluster score 0.017742 (lower is better)

Here is the balancer configuration of upmap_max_deviation:
# ceph config get mgr mgr/balancer/upmap_max_deviation
5

We have two different types of OSDS, one is 7681G and another is 3840G. When I 
checked our PG distribution on each type of OSD, I found the PG distribution is 
not evenly, for the 7681G OSDs, the OSD distribution varies from 136 to 158; 
while for the 3840G OSDs, it varies from 60 to 83, seems the 
upmap_max_deviation is almost +/- 10. So I just wondering if this is expected 
or do I need to change the upmap_max_deviation to a smaller value.

Thanks for answering my question.
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[ceph-users] Question about PG mgr/balancer/crush_compat_metrics

[bryansoong21]

Hello,

We are using a Ceph Pacific (16.2.10) cluster and enabled the balancer module, 
but the usage of some OSDs keeps growing and reached up to 
mon_osd_nearfull_ratio, which we use 85% by default, and we think the balancer 
module should do some balancer work.

So I checked our balancer configuration and found that our 
"crush_compat_metrics" is set to "pgs,objects,bytes", and this three values are 
used in src.pybind.mgr.balancer.module.Module.calc_eval. However, when doing 
the actual balance task, only the first key is used to do the auto balance, in 
src.pybind.mgr.balancer.module.Module.do_crush_compat:
metrics = self.get_module_option('crush_compat_metrics').split(',')
key = metrics[0] # balancing using the first score metric

My concern is, any reason why we calculate the balancing using the three items 
but only do the balance using the first one?

Thanks.
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