Ceph

The 'osd crush reweight ...' command only lets you reweight a single item. In a large cluster, it may be helpful to slowly bring an entire host, rack, or DC online, and adjusting the crush weights across many devices is tedious and error-prone.

This would let you specify a subtree node (like a host or rack) and would set the weight for every leaf item contained beneath that point.

This came up during an in-depth architecture discussion for a very large scale deployment.