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 a priority order depending on whether or not the source and the target storage reside in the same rack.

The Balancer uses the following priority orders for pairing storage groups from the source and the target.

• 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