Migrating data from a large extent pool to a small extent pool

A computer program product for migrating data from a large extent pool to a small extent pool, the computer program product comprising a computer readable storage medium having program instructions embodied therewith, the program instructions executable by a processor to cause the processor to perform a method comprising:

• identifying, utilizing the processor, a request to migrate data associated with a volume from a source storage pool to a destination storage pool;
• identifying, utilizing the processor, VST entries corresponding to rank extents within the source storage pool containing the data;
• allocating and synchronizing, utilizing the processor, small VSTs for each of the identified VST entries within the volume;
• allocating, utilizing the processor, one or more rank extents within the destination storage pool;
• transferring, utilizing the processor, the data associated with the volume from the rank extents within the source storage pool containing the data to the one or more rank extents in the one or more ranks of the destination storage pool;
• updating, utilizing the processor, the small VSTs to correspond to the transferred data in the one or more rank extents in the one or more ranks of the destination storage pool;
• and
• freeing, utilizing the processor, the data from the one or more rank extents within the source storage pool.