Patent ID: 8656122

Claim:
A method for managing data in a first storage and a second storage, comprising: processing an operation to migrate an extent of tracks from the second storage to the first storage; determining whether an extent object exists for the extent to migrate, wherein the extent object exists if the extent was previously migrated from the first storage to the second storage at a previous time, and wherein the extent object includes for each track a write indicator indicating whether the track was updated in the second storage since the previous time when the extent was previously migrated to the second storage; and in response to determining that the extent object exists, performing: determining the tracks in the extent having the write indicator indicating that the track was updated in the second storage since the previous time; copying the data for the determined tracks from the second storage to free locations in the first storage; and for each determined track, update the entry for the determined track in the extent object to indicate the free location to which the data for the track was copied as an active address for the track.