Crushmap ruleset for rack aware PG placement

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Hi Daniel,

When I run

crushtool --outfn crushmap --build --num_osds 100 host straw 2 rack straw 10 default straw 0
crushtool -d crushmap -o crushmap.txt
cat >> crushmap.txt <<EOF
rule myrule {
	ruleset 1
	type replicated
	min_size 1
	max_size 10
	step take default
	step choose firstn 2 type rack
	step chooseleaf firstn 2 type host
	step emit
}
EOF
crushtool -c crushmap.txt -o crushmap
crushtool -i crushmap --test --show-utilization --rule 1 --min-x 1 --max-x 10 --num-rep 3

I get

rule 1 (myrule), x = 1..10, numrep = 3..3
CRUSH rule 1 x 1 [79,69,10]
CRUSH rule 1 x 2 [56,58,60]
CRUSH rule 1 x 3 [30,26,19]
CRUSH rule 1 x 4 [14,8,69]
CRUSH rule 1 x 5 [7,4,88]
CRUSH rule 1 x 6 [54,52,37]
CRUSH rule 1 x 7 [69,67,19]
CRUSH rule 1 x 8 [51,46,83]
CRUSH rule 1 x 9 [55,56,35]
CRUSH rule 1 x 10 [54,51,95]
rule 1 (myrule) num_rep 3 result size == 3:	10/10

What command are you running to get a core dump ?

Cheers

On 16/09/2014 12:02, Daniel Swarbrick wrote:
> On 15/09/14 17:28, Sage Weil wrote:
>>
>> rule myrule {
>> 	ruleset 1
>> 	type replicated
>> 	min_size 1
>> 	max_size 10
>> 	step take default
>> 	step choose firstn 2 type rack
>> 	step chooseleaf firstn 2 type host
>> 	step emit
>> }
>>
>> That will give you 4 osds, spread across 2 hosts in each rack.  The pool 
>> size (replication factor) is 3, so RADOS will just use the first three (2 
>> hosts in first rack, 1 host in second rack).
> 
> I have a similar requirement, where we currently have four nodes, two in
> each fire zone, with pool size 3. At the moment, due to the number of
> nodes, we are guaranteed at least one replica in each fire zone (which
> we represent with bucket type "room"). If we add more nodes in future,
> the current ruleset may cause all three replicas of a PG to land in a
> single zone.
> 
> I tried the ruleset suggested above (replacing "rack" with "room"), but
> when testing it with crushtool --test --show-utilization, I simply get
> segfaults. No amount of fiddling around seems to make it work - even
> adding two new hypothetical nodes to the crushmap doesn't help.
> 
> What could I perhaps be doing wrong?
> 
> _______________________________________________
> ceph-users mailing list
> ceph-users at lists.ceph.com
> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
> 

-- 
Lo?c Dachary, Artisan Logiciel Libre

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