Hi Gregory,
Thanks for the direction that I  finish with 3 different rule in a ruleset for 
different rep size:
Tested no bad-mapping and host / osd are correctly balanced between 2 chassis.

Not sure if it can be optimized but I am happy with current result:
rule rule_rep2 {
ruleset 0
type replicated
min_size 2
max_size 2
step take chassis1
step chooseleaf firstn 1 type host
step emit
step take chassis2
step chooseleaf firstn 1 type host
step emit
}
rule rule_rep34 {
ruleset 0
type replicated
min_size 3
max_size 4
step take default
step choose firstn 2 type chassis
step chooseleaf firstn 2 type host
step emit
}
rule rule_rep56 {
ruleset 0
type replicated
min_size 5
max_size 6
step take default
step choose firstn 3 type chassis
step chooseleaf firstn 3 type host
step emit
}


Luke

From: Gregory Farnum [mailto:g...@gregs42.com]
Sent: Friday, February 13, 2015 11:01 PM
To: Luke Kao; ceph-users@lists.ceph.com
Subject: Re: [ceph-users] CRUSHMAP for chassis balance

With sufficiently new CRUSH versions (all the latest point releases on LTS?) I 
think you can simply have the rule return extra IDs which are dropped if they 
exceed the number required. So you can choose two chassis, then have those both 
choose to lead OSDs, and return those 4 from the rule.
-Greg
On Fri, Feb 13, 2015 at 6:13 AM Luke Kao 
<luke....@mycom-osi.com<mailto:luke....@mycom-osi.com>> wrote:
Dear cepher,
Currently I am working on crushmap to try to make sure the at least one copy 
are going to different chassis.
Say chassis1 has host1,host2,host3, and chassis2 has host4,host5,host6.

With replication =2, it’s not a problem, I can use the following step in rule
step take chasses1
step chooseleaf firstn 1 type host
step emit
step take chasses2
step chooseleaf firstn 1 type host
step emit

But for replication=3, I tried
step take chasses1
step chooseleaf firstn 1 type host
step emit
step take chasses2
step chooseleaf firstn 1 type host
step emit
step take default
step chooseleaf firstn 1 type host
step emit

At the end, the 3rd osd returned in rule test is always duplicate with first 1 
or first 2.

Any idea or what’s the direction to move forward?
Thanks in advance

BR,
Luke
MYCOM-OSI


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