Step 2: Storage Group Pairing
The HDFS Balancer selects over-utilized or above-average storage as source storage, and under-utilized or below-average storage as target storage. It pairs a source storage group with a target storage group (source → target) in the following priority order:
Same-Rack (where the source and the target storage reside in the same rack)
Over-Utilized → Under-Utilize
Over-Utilized → Below-Average
Above-Average → Under-Utilized
Any (where the source and target storage do not reside in the same rack)
Over-Utilized → Under-Utilized
Over-Utilized → Below-Average
Above-Average → Under-Utilized