The documented approach to stopping the shard balancer is to use the "sh.setBalancerState(false)" command on the mongos. However the command can also be run on any mongod, and no exception is raised.

This is because the the command successfully writes to the local config, but this is nonsensical on a mongod. This can mislead the user into thinking the command has given the desired result.

This server request is to add some exception handling to help prevent this confusion.