Data-storage volumes, such as a file system on a storage system, may utilize a particular operating system format. Converting a data-storage volume to a different format may be desirable at times. However, this can be time consuming and resource intensive if data needs to be copied. Accordingly, substantially copying-free, in-place conversion of a data-storage volume from a first format to a second format is provided herein. In one embodiment, a data-storage volume may be converted from a first format to a second format while the data-storage volume is mounted and/or without copying data within the data-storage volume to a separate data-storage volume. Before conversion, features associated with the first format and the second format may be compared to detect incompatibilities that may result from conversion. During conversion, access to the data-storage volume may be blocked. Upon successful conversion, various post conversion operations may be performed.