There isn’t an easy way to determine where the data is currently being read from. In theory you can examine the subscription cursor to determine the segment being read and then look at the specific segment’s data in the stats to see if it has been offloaded or not.

Once a segment is offloaded to tiered-storage, the data remains on BK for a few hours, IIRC there is a configuration setting for this that defaults to 4 hours. After that, the segments are marked for deletion and removed via the BookKeeper garbage collection process. So long story short, it could take quite a bit of time before the disk space on the bookies is reclaimed, but you can adjust the behavior to be more aggressive if needed.

The information I read here leads me to a misunderstanding，It makes me think storageSize and offloadedStorageSize are two separate metrics