Re: CRUSH depends on host + OSD?

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Hi,

October 15 2014 7:05 PM, "Chad Seys" <cwseys@xxxxxxxxxxxxxxxx> wrote: 
> Hi Dan,
> I'm using Emperor (0.72). Though I would think CRUSH maps have not changed
> that much btw versions?

I'm using dumpling, with the hashpspool flag enabled, which I believe could have been the only difference.

>> That sounds bizarre to me, and I can't reproduce it. I added an osd (which
>> was previously not in the crush map) to a fake host=test:
>> 
>> ceph osd crush create-or-move osd.52 1.0 rack=RJ45 host=test
> 
> I have flatter failure domain with only servers/drives. Looks like you would
> have at least rack/server/drive. Would that make the difference?

Could be. Now I just tried using testrack, testhost then removing the osd. So I have

-30     0                       rack testrack
-23     0                               host testhost

Then I remove testhost and testrack and there is still no data movement afterwards. Our crush rule is doing

rule data {
        ruleset 0
        type replicated
        min_size 1
        max_size 10
        step take default
        step chooseleaf firstn 0 type rack
        step emit
}

in case that makes a difference.

> 
>> As far as I've experienced, an entry in the crush map with a _crush_ weight
>> of zero is equivalent to that entry not being in the map. (In fact, I use
>> this to drain OSDs ... I just ceph osd crush reweight osd.X 0, then
>> sometime later I crush rm the osd, without incurring any secondary data
>> movement).
> 
> Is the crush weight the second column of ceph osd tree ?

Yes, that's the one I'm talking about. The reweight (0-1 value in the rightmost column) is another thing altogether.

Cheers, Dan

> I'll have to pay attention to that next time I drain a node.
> 
> Thanks for investigating!
> Chad. 
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