| Act | Description |
| A | IO was remapped to a different device |
| B | IO bounced |
| C | IO completion |
| D | IO issued to driver |
| F | IO front merged with request on queue |
| G | Get request |
| I | IO inserted onto request queue |
| M | IO back merged with request on queue |
| P | Plug request |
| Q | IO handled by request queue code |
| S | Sleep request |
| T | Unplug due to timeout |
| U | Unplug request |
| X | Split |