21 Jul
2020
21 Jul
'20
7:01 p.m.
Marcel;
Short answer; yes, it might be expected behavior.
PG placement is highly dependent on the cluster layout, and CRUSH rules. So... Some
clarifying questions.
What version of Ceph are you running?
How many nodes do you have?
How many pools do you have, and what are their failure domains?
Thank you,
Dominic L. Hilsbos, MBA
Director - Information Technology
Perform Air International, Inc.
DHilsbos(a)PerformAir.com
www.PerformAir.com
-----Original Message-----
From: Marcel Kuiper [mailto:ceph@mknet.nl]
Sent: Tuesday, July 21, 2020 6:52 AM
To: ceph-users(a)ceph.io
Subject: [ceph-users] osd out vs crush reweight
Hi list,
I ran a test with marking an osd out versus setting its crush weight to 0.
I compared to what osds pages were send. The crush map has 3 rooms. This
is what happened.
On ceph osd out 111 (first room; this node has osds 108 - 116) pg's were
send to the following osds
NR PG's OSD
2 1
1 4
1 5
1 6
1 7
2 8
1 31
1 34
1 35
1 56
2 57
1 58
1 61
1 83
1 84
1 88
1 99
1 100
2 107
1 114
2 117
1 118
1 119
1 121
All PG's were send to osds on other nodes in the same room, except for 1
PG on osd 114. I think this works as expected
Now I marked the osd in and wait until all stabilized. Then I set the
crush weight to 0. ceph osd crush reweight osd.111 0. I thought this
lowers the crush weight of the node so even less chances that PG's end up
on an osd of the same node. However the result are
NR PG's OSD
1 61
1 83
1 86
3 108
4 109
5 110
2 112
5 113
7 114
5 115
2 116
except for 3 PG's all other PG's ended up on an osd belonging to the same
node :-O. Is this expected behaviour? Can someone explain?? This is on
nautilus 14.2.8.
Thanks
Marcel
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