Description of problem:

The current documentation here: https://access.qa.redhat.com/documentation/en/red-hat-ceph-storage/2/single/installation-guide-for-red-hat-enterprise-linux#installing_red_hat_ceph_storage_using_ansible

In the section 3.2.4. Configuring Ceph OSD Settings

recommends on 3. to "Uncomment the crush_location setting and the osd_crush_location setting."

This flag should be uncommented only on a very special circonstance while playing with complex CRUSH maps.

For example, there are cases where we are collocating different devices (rotational and non-rotational drives) on the same machine and we want to separate them into different pool just as described in this article: https://www.sebastien-han.fr/blog/2014/08/25/ceph-mix-sata-and-ssd-within-the-same-box/

In this scenario you might want to force the location of some OSDs. By updating this variable osd_crush_location you can set a preferred location.

Not that this is not ideal, since this will trigger some changes into the ceph.conf, making it a bit inconsistent with what was generated, so it's NOT recommend to use this option unless you really have a unique scenario.



 

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