Improve documentation for druid.coordinator.balancer.strategy option

[rafitadiaz]

I see that in the configuration reference for the option druid.coordinator.balancer.strategy is mention that:

• diskNormalized weights the costs according to the servers' disk usage ratios - there are known issues with this strategy distributing segments unevenly across the cluster.
• random distributes segments among services randomly.

And then says that the default is cost.

What is cost? Cost base on what? Where can we find a reference on the documentation explaining the differences between 3 strategies?

It would be great a brief explanation of what is the cost strategy and why is the default

[kfaraz]

Thanks for reporting this issue, @rafitadiaz !

I have created a PR #17595 to improve the docs.
You can see a preview here: https://github.com/apache/druid/blob/1105837763e7da29fba9f430dbe45d7d01618b5d/docs/design/coordinator.md#balancing-segments-in-a-tier

[rafitadiaz]

Ooohhh. Thanks 🙏🙏🙏🙏

This is super helpful and very well explained.

Thanks for the update!!!!