On 05/27/2014 03:55 PM, Sahana wrote:
> HI all,
>
> Recently I was playing with crushmaps. I would like to know the
> difference between step choose and step chooseleaf.
>
> when I used :
>
> ruleset rule1{
>
> ...
> step take default
> step choose firstn 0 host
> step emit
> }
>
> And I tested above using crushtool, it returned ids of bucket host.
>
You want to have devices/osds to place your data on.
> But when I used it in cluster, it chose osds.
>
> If this works to get devices, then why we need chooseleaf.
>
Chooseleaf goes into that leaf and keeps searching until it finds a
device. Choose only goes down only leaf and doesn't keep searching
deeper into the tree.
In most situation chooseleaf is sufficient.
> Regards
> Sahana.
>
>
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--
Wido den Hollander
Ceph consultant and trainer
42on B.V.
Phone: +31 (0)20 700 9902
Skype: contact42on
