Tablet metadata and consensus metadata are placed in the first configured data directory. This is an issue, as every write to these metadata incurs an fsync and this stresses the first disk considerably more than the others
One way around this is to spread metadata across multiple data directories. A natural choice would be to place them in a directory within the tablet's disk group. In this way, the data/metadata can be completely localized to the disk group, which has the added benefit of making the risk of disk failures easier to assess per tablet.