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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