This setting allows matching of indices by their age and the space they consume. In other words, it sorts all indices in the list by age, then starts adding the space consumed by each index, beginning from the youngest. Once the value of disk_space is reached, all remaining indices, which are the oldest, will remain in the actionable list, omitting all of the younger indices.
The default value of this setting is
Use of this setting requires the additional setting, source.