Head–disk interface (HDI) degradation risk reduction in hard disk drive (HDD) during thermal asperity (TA) track follow mapping and seeking

Abstract

HDD heads have various interaction modes with thermal asperities (TAs), and protection mechanisms need to be put in place to ensure the head–disk interaction (HDI) resulting from them is eliminated or minimized to the highest extent possible. We propose a method to reduce such head–disk interaction (HDI) during TA detection and classification by flying higher at low thermal fly-height control (TFC) power, which minimizes the interaction of the TA with the head. The key idea is to scan the head at higher fly height, but with higher ECS bias voltage. By mapping out these TAs and ensuring the head does not fly over them again to prevent HDI, the fly height can then be lowered, and the rest of the TA cluster can be scanned. Following this method iteratively, the entire TA cluster can be mapped out with minimal interaction with the head. Although this method entails an increase in the test time to detect and map all TAs, compared to detecting them with TFC being on, this can help improve the reliability of the drive by protecting the sensitive read/write elements especially for energy assisted recording from HDI. Other than track follow, TA interactions also occur when the head seeks across the tracks. Typical seek avoidance attempts to eliminate TA interaction during seeking, however it is not straightforward to determine which of the seek mechanism: TFC on during short seeks, retract/arrival during long seeks, interaction with high TAs (HTAs), whose height is more than the fly height of the head during long seeks with TFC off, or idle TA interaction causes the greatest HDI. Through theoretical analysis and experimental corroboration, this paper intends to rank the various modes of TA interaction, so by developing features for eliminating or minimizing them in that order could help bring the maximum benefit for achieving minimum lifetime reduction of the head due to such interaction.