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.[1] 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.[2][3][4]: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.[4]:11 ff.[5]
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.[1] In September 2014, HGST announced a 10 TB drive filled with helium that uses host-managed shingled magnetic recording,[6] although in December 2015 it followed this with a 10 TB helium-filled drive that uses conventional non-shingled perpendicular recording.[7]
See also
References
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External links
- LSFMM: A storage technology update, LWN.net, April 23, 2013, by Jonathan Corbet
- SMR Impact on Linux Storage Subsystem, HGST, 2014, by Jorge Campello and Adam Manzanares
- Layout optimisation for using XFS on host-managed SMR drives, March 2015
- SMR in Linux Systems, Seagate, March 18, 2015, by Adrian Palmer
- Host-Aware SMR, Seagate, November 10, 2014, by Timothy Feldman
- Disks for Data Centers, Google, 2016, by Eric Brewer, Lawrence Ying, Lawrence Greenfield, Robert Cypher, and Theodore T'so
