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

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The 40,000 foot view

To visually see the overall topology of a Ceph cluster, run ceph osd tree. This will show us at once the hierarchy of CRUSH buckets, including the name of each bucket, the weight, whether it is marked up or down, a weight adjustment, and an advanced attribute of primary affinity. This cluster was provisioned initially with 3 racks each housing 4 hosts for a total of 12 OSD nodes. Each OSD node (also known as host, also known as server) in turn houses 24 OSD drives.

    # ceph osd tree
    ID  WEIGHT    TYPE NAME           UP/DOWN REWEIGHT PRIMARY-AFFINITY
     -1 974.89661 root default
    -14 330.76886     rack r1
     -2  83.56099         host data001
      0   3.48199             osd.0       up  1.00000          1.00000
    ...
     23   3.48199             osd.23      up  1.00000          1.00000
     -3  80.08588         host data002
     24 3.48199 ...

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