Currently we need sharding solely for write distribution (due to high write lock contention). Due to the fact that these writes happen on relatively small collections automatic sharding fails because collections may never top even 10mb in size so chunks are never split, and therefore never moved across shards. I'm aware we could use even smaller chunk sizes to force the issue but I was led to understood frequent chunk migrations come with significant overhead.

I was wondering if it's possible to add a balancing strategy that would reserve a chunk on each available shard for a collection and start distributing writes. Chunk moves/splits should only occur if additional shards are added and/or the chunk size exceeds a specific size (the current strategy, basically).

I'm not sure if I'm explaining this right but basically what I want is :
1) Distributes writes from the very first update/insert
2) Rebalanced when shards are added or removed

Hope it makes sense. If there's a solution available to reach the same goal that doesn't involve manual admin I'd be interested in hearing it. Thanks