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Hard disk drive (HDD) is a mechanical data storage device with head slider flying over disk medium surface. The head medium spacing keeps reducing for the sake of linear density increment. The head flying height (FH) in HDD product is reduced to less than 1 nm of back-off spacing. The intermittent head disk contact happens in HDD and causes additional head motions in 3-dimensions: FH, off-track, and jitter. Increasing FH deteriorates the BER performance. The off-track motion causes track squeeze of adjacent track during writing process and has the potential to loss data in squeezed track. Head jitter motion makes the synchronous writing more challenged for bit patterned medium. It is desired to measure head 3D motion inside HDD.

Recently, the announcement of the first 8 TB shingled drive to be available commercially for archival purposes by Seagate [1]. In shingled magnetic recording (SMR), a wider writer is able to write narrower track for pushing higher track density. At narrower track width, the jitter noise increases and it results in lower on-track SNR. Usually, the linear density is reduced in SMR and the areal density gain comes from more track density increment. Comparing to PMR, the SMR is able to increase the areal density by 15% to 30% depending on the servo performance of the drive. At reduced linear density, there is a big jump in track density.

Currently, the areal density grow in HDD still depends on the reduction of grain number per bit. In order to have less SNR penalty, it has to scale more on the track density rather than the linear density. This work proposed to insert an additional servo recording layer between data recording layer and SUL of conventional PMR media. With high quality continuous servo signals, the dedicated servo recording system has better servo performance than the conventional embedded servo for the same servo mechanics. This guarantees the high track density requirement of magnetic recording system.