Permanent deletion of a Druid segment has two steps:
1. The segment must first be marked as "unused". This occurs when a segment is dropped by retention rules, and when a user manually disables a segment through the Coordinator API.
2. After segments have been marked as "unused", a Kill Task will delete any "unused" segments from Druid's metadata store as well as deep storage.
For documentation on retention rules, please see [Data Retention](../operations/rule-configuration.html).
For documentation on disabling segments using the Coordinator API, please see [Coordinator Delete API](../operations/api-reference.html#coordinator-delete)
A data deletion tutorial is available at [Tutorial: Deleting data](../tutorials/tutorial-delete-data.html)
## Kill Task
Kill tasks delete all information about a segment and removes it from deep storage. Killable segments must be disabled (used==0) in the Druid segment table. The available grammar is: