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Learning Ceph - Second Edition by Karan Singh, Vaibhav Bhembre, Anthony D'Atri

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OSD CRUSH map

The CRUSH map holds a variety information necessary for Ceph to distribute and place objects. Sometimes it is useful to find out if this distribution isn't working properly because of a wrong value in the CRUSH map. The CRUSH map can be downloaded as a file in binary format that we decompile locally for viewing. It is also possible to dump the CRUSH map and rules directly from the command line, which is expedient for a quick check.

We can use osd crush dump to display the entire CRUSH map.

root@ceph-client0:~# ceph osd crush dump{"devices": [{"id": 0,"name": "osd.0"},..."rules": [{"rule_id": 0,"rule_name": "replicated_ruleset","ruleset": 0,..."tunables": {"choose_local_tries": 0,"choose_local_fallback_tries": 0,"choose_total_tries": ...

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