A thin provisioning storage system is able to present a thin provisioned volume to a computer, such that the computer stores data to the volume as if storage space on disk drives was already allocated for the volume. Upon receiving a write request from the computer, in which the write request is directed to an area of the volume for which storage space on the disk drives has not yet been allocated, the storage system allocates new space on the disk drives. When allocating the new space, the storage system obtains a designated performance level for the volume, and determines a number of storage extents to be allocated to the volume based upon the determined performance level. The storage system also is able to take into account performance metrics for the disk drives and/or array groups when selecting locations from which to allocate the storage extents.