A computer-implemented method, according to one approach, is for converting an existing storage pool into an intended storage pool in place. The computer-implemented method includes: identifying a request to convert the existing storage pool having a first extent size into the intended storage pool having a second extent size, where the first extent size is larger than the second extent size. For each volume in the existing storage pool: a temporary pause/lock is performed on a volume segment table (VST) entry which corresponds to the given volume, and a new structure is applied to the VST entry. The new structure divides existing physical extents associated with the VST entry into two or more smaller physical extents. Furthermore, for each of the ranks in the existing storage pool, the given rank is converted from the first extent size to the second extent size.