Replica assignment with rack awareness

Hi,

I wanted to confirm the behavior when a new topic is created in a cluster
where brokers have rack.id parameter configured.

Lets say we have a 6 broker cluster

3 brokers with rack.id 'RACK1' ( broker ids : 1,2,3 )
3 brokers with rack.id 'RACK2' ( brokers ids : 4,5,6 )

I created a topic with replication factor 4

Partition 0 :

Replica set = 1,4,2,5
( equal distribution of replicas across racks )

Will replicas always be equally distributed across racks or it can be
uneven also

like:

Replica set = 1,4,2,3

uneven distribution of replicas across racks.
1,2,3 are from same rack


thanks,
ashish