Shingled magnetic recording

Shingled magnetic recording (SMR) is a magnetic storage data recording technology used in hard disk drives (HDDs) to increase storage density and overall per-drive storage capacity. Conventional hard disk drives record data by writing non-overlapping magnetic tracks parallel to each other (perpendicular recording), while shingled recording writes new tracks that overlap part of the previously written magnetic track, leaving the previous track narrower and allowing for higher track density. Thus, the tracks partially overlap similar to roof shingles. This approach was selected because physical limitations prevent recording magnetic heads from having the same width as reading heads, leaving recording heads wider.:7–9 The overlapping-tracks architecture may slow down the writing process since writing to one track overwrites adjacent tracks, and requires them to be rewritten as well. Device-managed SMR devices hide this complexity by managing it in the firmware, presenting an interface like any other hard disk, while other SMR devices are host-managed and depend on the operating system to know how to handle the drive, and only write sequentially to certain regions of the drive.:11 ff. Seagate has been shipping device-managed SMR hard drives since September 2013, while referring to an increase in overall hard disk drive capacity of about 25%, compared to non-shingled storage. In September 2014, HGST announced a 10 TB drive filled with helium that uses host-managed shingled magnetic recording, although in December 2015 it followed this with a 10 TB helium-filled drive that uses conventional non-shingled perpendicular recording.. In November 2018, HGST introduced 14- and 15-TB drives There are three different ways that data can be managed on an SMR drive: A Device Managed drive appears to the host identically to a non-shingled drive. It is not necessary for the host to follow any special protocols. All handling of data, as it relates to the shingled nature of the storage, is managed by the device. In addition, the host is unaware that the storage is shingled. A Host Managed device requires strict adherence to a special protocol by the host. Since the host manages the shingled nature of the storage, it is required to write sequentially so as to not destroy existing data. The drive will refuse to execute commands which violate this protocol. Host Aware is a combination of Drive Managed and Host Managed. The drive is capable of managing the shingled nature of the storage and will execute any command the host gives it, regardless of if it is sequential or not. However, the host is aware that the drive is shingled, and able to query the drive for fill levels. This allows the host to optimize writes for the shingled nature, while also allowing the drive to be flexible and backwards-compatible. While for traditional SMR models each zone is assigned a type at manufacture time, dynamic hybrid SMR drives allow to reconfigure the zone type from shingled to conventional and back by the customer.