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When users disable tiered storage on a topic, the tiered storage state on a topic transitions through the following stages: ENABLED → DISABLING → DISABLED.

ENABLED
The ENABLED  state represents when tiered storage is enabled on a topic or when it has been re-enabled after disablement. In this state, the RemoteLogManager (RLM) has scheduled a task for the topic-partitions with the RemoteLogManager thread pool and RemoteStorageFetcher thread pool. The possible state transition from the ENABLED  state is to the DISABLING  state.

DISABLING
When users initiate an alter config API call to disable tiered storage on a topic that is currently in the ENABLED  state, the topic enters the DISABLING  state. In this state, various tasks are performed asynchronously to complete the disablement process. These tasks include:

• Cancel tasks for the topic-partitions from the RemoteLogManager thread pool to stop archiving logs to the remote storage.
• If the disablement was triggered with the remote.log.disable.policy=delete option, draining fetch requests in RemoteFetchPurgatory and block new fetch requests from getting added to the RemoteStorageFetcher thread pool.
• If the disablement was triggered with the remote.log.disable.policy=retain option, we will cancel the tasks for the topic-partitions from the RemoteLogManager thread pool only for stopping archiving logs but the task for expiring remote segments will continue to work. The fetch requests from remote storage will also continue to work after disablement

While the topic is in the DISABLING state, new alter config API calls to disable tiered storage will be rejected. The possible state transition from the DISABLING state is to the DISABLED state.

DISABLED
The DISABLED state represents when tiered storage is fully disabled on a topic. In this state, the RLM does not have any scheduled tasks for the topic-partitions in the RemoteLogManager thread pool for copying segments to remote storage. If the topic was disabled with the remote.log.disable.policy=delete option, all remote data is marked for deletion and it is inaccessible for read. If the topic was disabled with the remote.log.disable.policy=retain option, there will be tasks scheduled for the topic-partitions only for expiration of remote logs but not for copying logs to remote storage. The RemoteStorageFetcher thread pool will also continue to accept remote fetch requests. The possible state transition from DISABLED state is to the ENABLED.