RocketMQ broker stores all messages before they are expired, which requires pretty much storage for a high load system. For now, the message store can be configured to use only one partition. Quite often, we find broker runs out of storage as business expands quickly. Online resizing a partition most of time is not possible(with absence of LVM) whilst attaching a new disk/partition in cloud environment is super easy.
It would be nice for RocketMQ to be capable of adding extra commit log store path online, allocating commit log files onto partitions based on free/available space.