The patent's assignee for patent number 8510504 is
News editors obtained the following quote from the background information supplied by the inventors: "Conventional disk drives with magnetic media organize data in concentric tracks. The concept of shingled writing is a form of perpendicular magnetic recording and has been proposed as a way of increasing the areal density of magnetic recording. In shingle-written magnetic recording (SMR) media a region (band) of adjacent tracks are written so as to overlap one or more previously written tracks. Unlike conventional tracks, which can be written in any order, the shingled tracks must be written in sequence. The tracks on an SMR disk surface are organized into a plurality of shingled regions (typically called I-regions) which can be written sequentially from an inner diameter (ID) to an outer diameter (OD) or from OD to ID. The number of tracks shingled together in a region is a key performance parameter of shingled-writing. Once written in shingled structure, an individual track cannot be updated in place, because that would overwrite and, thereby, destroy the data in overlapping tracks. Shingle-written data track regions, therefore, from the user's viewpoint are sometimes thought of as append-only logs. To improve the performance of SMR drives, a portion of the media is allocated to a so-called 'exception region' (E-region) which is used as staging area for data which will ultimately be written to an I-region. After an I-region is written, updates or deletes to LBAs in the region cannot be written directly, so the old data becomes a virtual hole in the region which is subject to being defragmented to remove the virtual holes and make room for more exceptions in the E-region. The indirection controller hardware and firmware execute this process.
"Because a portion of the previously written track is over-written during writing of the adjacent track, SMR heads write a wider path than the final actual track width. Therefore, most of the write path is erased when the overlapping track is subsequently written. These unique aspects of SMR have led to the development of special write heads for SMR.
"Address indirection in the shingle-written storage device's internal architecture is useful to emulate existing host interfaces at least to some extent and shield the host from the complexities associated with SMR. Conventionally host file systems use logical block addresses (LBAs) in commands to read and write blocks of data without regard for actual locations (physical block address (PBA)) used internally by the storage device. Hard disk drives have had some level of LBA-PBA indirection for decades that, among other things, allows bad sectors on the disk to be remapped to good sectors that have been reserved for this purpose. Address indirection is typically implemented in the controller portion of the drive's architecture. The controller translates the LBAs in host commands to an internal physical address, or something closer to a physical address.
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