A method for determining storage medium transfer rate characteristics. A host computer system issues a sequence of read commands to a storage medium to determine an accurate mapping of differences in transfer rate characteristics. For example, the host issues a sequence of relatively large reads to the storage medium at successively higher logical cluster numbers (LCNs). The host waits for each read command to complete before issuing the next read command and tracks a time interval that is representative of the time between completions of read commands.