Method and apparatus for using block level quality of service (QOS) data in a data storage device. A memory space is provided with a plurality of physical data storage blocks, such as data sectors on a magnetic disc. The QOS data identify at least one QOS characteristic for each of the available blocks. Transfers of user data between the blocks and a host device are preferably carried out in relation to the QOS data. In some preferred embodiments, the QOS data identifies a certification state for each of the blocks. In this way, the device is manufactured with less than all of the blocks having been successfully certified, and the remaining blocks are certified by the device during field use. In other preferred embodiments, the QOS data include a virus scan status, an access history, a write status, or an overlapped track indication for each said block.