Re: Need help for PG problem

施柏安 <desmond.s@xxxxxxxxxxxxxx> · Thu, 24 Mar 2016 09:24:43 +0800

It seems that you only have two host in your crush map. But the default ruleset would separate the object by host.
If you set size 3 for pools, then there would be one object can't build because you only have two hosts.

2016-03-23 20:17 GMT+08:00 Zhang Qiang <dotslash.lu@xxxxxxxxx>:
And here's the osd tree if it matters.
ID WEIGHT   TYPE NAME       UP/DOWN REWEIGHT PRIMARY-AFFINITY 
-1 22.39984 root default                                      
-2 21.39984     host 10                                       
 0  1.06999         osd.0        up  1.00000          1.00000 
 1  1.06999         osd.1        up  1.00000          1.00000 
 2  1.06999         osd.2        up  1.00000          1.00000 
 3  1.06999         osd.3        up  1.00000          1.00000 
 4  1.06999         osd.4        up  1.00000          1.00000 
 5  1.06999         osd.5        up  1.00000          1.00000 
 6  1.06999         osd.6        up  1.00000          1.00000 
 7  1.06999         osd.7        up  1.00000          1.00000 
 8  1.06999         osd.8        up  1.00000          1.00000 
 9  1.06999         osd.9        up  1.00000          1.00000 
10  1.06999         osd.10       up  1.00000          1.00000 
11  1.06999         osd.11       up  1.00000          1.00000 
12  1.06999         osd.12       up  1.00000          1.00000 
13  1.06999         osd.13       up  1.00000          1.00000 
14  1.06999         osd.14       up  1.00000          1.00000 
15  1.06999         osd.15       up  1.00000          1.00000 
16  1.06999         osd.16       up  1.00000          1.00000 
17  1.06999         osd.17       up  1.00000          1.00000 
18  1.06999         osd.18       up  1.00000          1.00000 
19  1.06999         osd.19       up  1.00000          1.00000 
-3  1.00000     host 148_96                                   
 0  1.00000         osd.0        up  1.00000          1.00000

On Wed, 23 Mar 2016 at 19:10 Zhang Qiang <dotslash.lu@xxxxxxxxx> wrote:
Oliver, Goncalo, 
Sorry to disturb again, but recreating the pool with a smaller pg_num didn't seem to work, now all 666 pgs are degraded + undersized.
New status:
    cluster d2a69513-ad8e-4b25-8f10-69c4041d624d
     health HEALTH_WARN
            666 pgs degraded
            82 pgs stuck unclean
            666 pgs undersized
     monmap e5: 5 mons at {1=10.3.138.37:6789/0,2=10.3.138.39:6789/0,3=10.3.138.40:6789/0,4=10.3.138.59:6789/0,GGZ-YG-S0311-PLATFORM-138=10.3.138.36:6789/0}
            election epoch 28, quorum 0,1,2,3,4 GGZ-YG-S0311-PLATFORM-138,1,2,3,4
     osdmap e705: 20 osds: 20 up, 20 in
      pgmap v1961: 666 pgs, 1 pools, 0 bytes data, 0 objects
            13223 MB used, 20861 GB / 21991 GB avail
                 666 active+undersized+degraded

Only one pool and its size is 3. So I think according to the algorithm, (20 * 100) / 3 = 666 pgs is reasonable.

I updated health detail and also attached a pg query result on gist(https://gist.github.com/dotSlashLu/22623b4cefa06a46e0d4).

On Wed, 23 Mar 2016 at 09:01 Dotslash Lu <dotslash.lu@xxxxxxxxx> wrote:
Hello Gonçalo,

Thanks for your reminding. I was just setting up the cluster for test, so don't worry, I can just remove the pool. And I learnt that since the replication number and pool number are related to pg_num, I'll consider them carefully before deploying any data. 

On Mar 23, 2016, at 6:58 AM, Goncalo Borges <goncalo.borges@xxxxxxxxxxxxx> wrote:

Hi Zhang...

If I can add some more info, the change of PGs is a heavy operation, and as far as i know, you should NEVER decrease PGs. From the notes in pgcalc (http://ceph.com/pgcalc/):

"It's also important to know that the PG count can be increased, but NEVER decreased without destroying / recreating the pool. However, increasing the PG Count of a pool is one of the most impactful events in a Ceph Cluster, and should be avoided for production
 clusters if possible."

So, in your case, I would consider in adding more OSDs. 

Cheers

Goncalo

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