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