Servo detection and control considering servo pattern defects

Hard disk drive servo system needs to improve its error tolerance at a decreasing signal to noise ratio (SNR), including at elevated fly heights with lower SNR for servo seek operations than during read and write to support the areal density growth. This paper discusses a servo burst error reduction scheme which can effectively reduce burst pattern defect induced servo demodulation errors and enhance the servo burst SNR. We also discuss the significant RRO that needs to be reduced in a drive with pre-patterned servo such as discrete track media or bit patterned media.