Techniques for data migration of a storage system are described herein. According to one embodiment, for at least one of segments of a file to be migrated from a source storage tier to a target storage tier, a fingerprint of the segment is transmitted to the target storage tier. In response to a response received from the target storage tier indicating that the segment has not been stored in the target tier based on the fingerprint, a storage space of the target tier estimated for migrating the file is incremented. One or more segments of the file that have not been stored in the target tier are migrated if the one or more segments of the file fit in the target storage tier based on the estimated storage space of the target tier.