Shingled magnetic recording (SMR)
An HDD recording method that overlaps tracks like roof shingles to raise areal density at the cost of rewrite behavior.
SMR raises areal density by overlapping successive write tracks like roof shingles: the write head is wider than the final readable track, so each pass trims the previous track to a narrow band the narrower reader can still sense. Tracks are grouped into zones with inter-zone gaps so the wide writer does not bleed across zone boundaries. Reads stay random-access; modifying a sector typically requires rewriting the affected shingled band. Hosts see one of three interface models—drive-managed (firmware hides constraints), host-aware (optional ZAC/ZBC optimization), or host-managed (mandatory sequential writes at the write pointer). INCITS T10 ZBC and T13 ZAC standardize the host-visible zone models; drive-managed has no separate command set because it presents as a conventional disk. SMR fits sequential/archive/object tiers; unmanaged random-write pools often prefer CMR.
Relations
- related
- cmr, pmr, hm-smr, device-managed-smr, nearline-hdd
Advantages
- Higher areal density than conventional track layout on the same PMR platform.
Limitations
- Random rewrite patterns may require host or drive-managed band relocation.