From the InfluxDB Glossary doc:
A shard contains the actual encoded and compressed data, and is represented by a TSM file on disk.
If you’re interested in learning more about shards, you can check out my coworker @mschae16 post on Shards and Retention Policies.
The _internal.shard measurement will give you the size on disk of the various shards, but it will not give you information about the size of the Write-Ahead-Log (or Hinted-Handoff Queue if you’re running the Enterprise version) or metadata stored on disk.
You can have multiple databases on disk. What are you actually trying to monitor? Do you want to know the size of an individual database, or the total disk usage of InfluxDB?
