Physical shards: Actual database servers. Adding servers is expensive and disruptive.
Logical shards: Virtual partitions within physical servers. Start with many logical shards on few physical servers.
Example: logical shards on physical servers ( each). When you need more capacity, move logical shards to new physical servers.
Benefits:
- Rebalancing moves logical shards, not individual rows
- Plan for future growth without immediate cost
- Easier capacity planning
Rule of thumb: Create x more logical shards than you expect to need physical servers. Future-proof your sharding strategy.