Improving Reindex Performance in v5.6

Actually, I've just seen this: Shards Distribution in Multiple disks

It looks from the data that the one with seemingly fewer shards from my index has more data for other miscellaneous/internal indices (created by Kibana/Monitoring etc).

That sort of makes sense. It's useful to know. In future, for example, I'd hold off on installing kibana until my indices have spread their data nicely across all the disks.