Hi Ahsley,

The rule you indicated, with “step choose indep 0 type osd” should select 13 
different OSDs but not necessary on 13 different servers. So you should be able 
to test that on say 4 servers if you have ~4 OSDs per server.

To split the selected OSDs across 4 hosts, I think you would do something like:
“step take fourtb
step choose indep 4 type host
step choose indep 4 type osd
step emit”

Cheers,
Maxime


From: ceph-users <[email protected]> on behalf of Ashley 
Merrick <[email protected]>
Date: Thursday 2 March 2017 11:34
To: "[email protected]" <[email protected]>
Subject: [ceph-users] CrushMap Rule Change

Hello,

I am currently doing some erasure code tests in a dev environment.

I have set the following by “default”

rule sas {
        ruleset 2
        type erasure
        min_size 3
        max_size 13
        step set_chooseleaf_tries 5
        step set_choose_tries 100
        step take fourtb
        step choose indep 0 type osd
        step emit
}

As I am splitting the file into 13 chunks it is placing these across 13 
different OSD’s.

In the DEV environment I do not have 13 hosts to do full host replication, 
however I am sure I can change the crush map rule to try and split evenly 
across the 4 HOST I have.

I’m think I will need to tell it to pick 4 HOST’s, and then the second line to 
pick OSD’s, however as 13 does not divide by 4 exactly what would be the best 
way to lay out this crushmap rule?

Thanks,
Ashley
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