A computer-implemented method for determining performance shortfall in a storage system includes recording a log of I/O operations of a storage system, wherein each I/O operation includes associated operational parameters. The method prepares the storage system to perform a replay of a performance shortfall that occurred during a specified time frame. The method performs the replay on the storage system based at least on the log of I/O operations and the I/O operations' associated operational parameters for the specified time frame. The method identifies a cause for the performance shortfall during the specified time frame based at least on the difference between I/O performance measures of the replay and I/O performance measures for the specified time frame.