Re: A self test on the usage of 'step choose|chooseleaf'

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On Thu, Aug 23, 2018 at 4:11 PM Cody <codeology.lab@xxxxxxxxx> wrote:
Hi everyone,

As a newbie, I am grateful for receiving many helps from people on
this mailing list. I would like to quickly test my understanding on
'step choose|chooseleaf' and wish you could point out any of my
mistakes.

Suppose I have a following topology:

                 root=default
                           |
                datacenter=dc
     /                     |               \
row=a             row=b            row=c
    rack=a1          rack=b1          rack=c1
         host=a1.1       host=b1.1       host=c1.1
         host=a1.2       host=b1.2       host=c1.2
         host=a1.3       host=b1.3       host=c1.3
     rack=a2         rack=b2          rack=c2
         host=a2.1       host=b2.1       host=c2.1
         host=a2.2       host=b2.2       host=c2.2
         host=a2.3       host=b2.3       host=c2.3
     rack=a3         rack=b3          rack=c3
         host=a3.1       host=b3.1       host=c3.1
         host=a3.2       host=b3.2       host=c3.2
         host=a3.3       host=b3.3       host=c3.3

*each host has 3 OSDs.

Then,

1) a rule that makes 3 replicas with a row-level failure domain would be like:
...
step take default
step chooseleaf fisrtn 0 type row

2) a rule that makes 3 replicas in different racks within the same row:
...
step take default
step choose firstn 1 type row
step chooseleaf firstn 0 type rack

3) a rule that makes 3+2 EC with a host-level failure domain:
...
step take default
step chooseleaf indep 0 type host

Are the above three rules correct regarding the usage of 'step
choose|chooseleaf'?

Yes.




Thank you!

Regards,
Cody

Here are related references from the mailing list:
[1] http://lists.ceph.com/pipermail/ceph-users-ceph.com/2016-June/010370.html
[2] http://lists.ceph.com/pipermail/ceph-users-ceph.com/2018-August/029255.html
[3] http://lists.ceph.com/pipermail/ceph-users-ceph.com/2018-August/029148.html
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