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Ceph Cookbook - Second Edition by Karan Singh, Michael Hackett, Vikhyat Umrao

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 Jewel – CRUSH_TUNABLES5

The Jewel profile will improve CRUSH’s overall behavior by limiting the number PG mapping changes when an OSD is marked out of the cluster.

The following is the new tunable:

  • chooseleaf_stable: A recursive chooseleaf attempt will use a better value for an inner loop that greatly reduces the number of mapping changes when an OSD is marked out. The legacy value is 0, while the new value of 1 uses the new approach:
    • Migration impact: Changing this value on an existing cluster will result in a very large amount of data movement as almost every PG mapping is likely to change

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