Shingled magnetic recording

Partial updating of data is difficult with SMR. Data will be written to adjacent tracks that do not need to be rewritten.

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 concentric magnetic tracks (conventional magnetic recording, Perpendicular recording), while shingled recording writes new tracks that overlap part of the previously written magnetic track, leaving the previous track narrower and allowing higher track density. Thus, the tracks partially overlap similar to roof shingles. This approach was selected because, if the writing head is made too narrow, it cannot provide the very high fields required in the recording layer of the disk.[2][3][4][5]: 7–9 

The overlapping-tracks architecture complicates the writing process, since writing to one track also overwrites an adjacent track. If adjacent tracks contain valid data, they must be rewritten as well. As a result, SMR drives are divided into many append-only (sequential) zones of overlapping tracks that need to be rewritten entirely when full, resembling flash blocks in solid-state drives. Device-managed SMR devices hide this complexity by managing it in the firmware, presenting an interface like any other hard disk. 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.[5]: 11 ff. [6] While SMR drives can use DRAM, flash memory, and even a portion of their own platter reserved for use with CMR instead of SMR,[7] as a cache to improve writing performance, continuous writing of large amount of data is noticeably slower than with CMR drives.[8][9][10]

  1. ^ Anand Lal Shimpi (September 9, 2013). "Seagate to Ship 5TB HDD in 2014 using Shingled Magnetic Recording". AnandTech. Retrieved February 9, 2015.
  2. ^ Roger Wood (October 19, 2010). "Shingled Magnetic Recording and Two-Dimensional Magnetic Recording" (PDF). IEEE. Retrieved December 14, 2014.
  3. ^ "What is Shingled Magnetic Recording (SMR)?". storagereview.com. January 30, 2015. Retrieved February 9, 2015.
  4. ^ K. Shimomura, "Large-Capacity HDDs Applying SMR Technology for Data Centers", Toshiba Technology Review, Vol. 24, No. 6., pp. 12-16, Nov 2019
  5. ^ a b Mary Dunn; Timothy Feldman (September 22, 2014). "Shingled Magnetic Recording: Models, Standardization, and Applications" (PDF). Storage Networking Industry Association. Retrieved February 9, 2015.
  6. ^ Jake Edge (March 26, 2014). "Support for shingled magnetic recording devices". LWN.net. Retrieved December 14, 2014.
  7. ^ Taillac, Will (May 28, 2020). "WD Red SMR vs CMR Tested Avoid Red SMR". ServeTheHome. Retrieved February 13, 2023.
  8. ^ Shilov, Anton. "The Evolution of HDDs in the Near Future: Speaking with Seagate CTO, Mark Re". www.anandtech.com. Retrieved May 30, 2020.
  9. ^ Cite error: The named reference Salter was invoked but never defined (see the help page).
  10. ^ Alcorn, Paul. "Sneaky Marketing Redux: Toshiba, Seagate Shipping Slower SMR Drives Without Disclosure, Too". Tom’s Hardware. Retrieved April 17, 2020.