View source for Physics:Shingled magnetic recording

{{short description|High-density disk drive recording technology}}
[[File:SMR HDD Rewrite.png|thumb|right|upright=1.5|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|magnetic storage]] data recording technology used in [[Engineering:Hard disk drive|hard disk drive]]s (HDDs) to increase storage density and overall per-drive storage capacity.<ref name="anandtech-7290">{{cite web |url=http://www.anandtech.com/show/7290/seagate-to-ship-5tb-hdd-in-2014-using-shingled-magnetic-recording/ |publisher=[[AnandTech]]| title=Seagate to Ship 5TB HDD in 2014 using Shingled Magnetic Recording |author=Anand Lal Shimpi |date=September 9, 2013 |accessdate=February 9, 2015}}</ref> Conventional hard disk drives record data by writing non-overlapping magnetic tracks parallel to each other (conventional magnetic recording, CMR), 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 [[Engineering:Roof shingle|roof shingle]]s. 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.<ref>{{cite web |url=http://www.ewh.ieee.org/r6/scv/mag/MtgSum/Meeting2010_10_Presentation.pdf |title=Shingled Magnetic Recording and Two-Dimensional Magnetic Recording |author=Roger Wood |website=ewh.ieee.org |date=October 19, 2010 |accessdate=December 14, 2014 }}</ref><ref>{{cite web |url=https://www.storagereview.com/news/what-is-shingled-magnetic-recording-smr |title=What is Shingled Magnetic Recording (SMR)? |website=storagereview.com |date=January 30, 2015 |accessdate=February 9, 2015}}</ref><ref>[https://www.toshiba.co.jp/tech/review/2019/06/74_06pdf/a04.pdf K. Shimomura, "Large-Capacity HDDs Applying SMR Technology for Data Centers", Toshiba Technology Review, Vol. 24, No. 6., pp. 12-16, Nov 2019]</ref><ref name="snia-smr">{{cite web
 | url = http://www.snia.org/sites/default/files/Dunn-Feldman_SNIA_Tutorial_Shingled_Magnetic_Recording-r7_Final.pdf
 | title = Shingled Magnetic Recording: Models, Standardization, and Applications
 | date = September 22, 2014 | accessdate = February 9, 2015
 | author1 = Mary Dunn | author2 = Timothy Feldman
 | publisher = [[Organization:Storage Networking Industry Association|Storage Networking Industry Association]]
 }}</ref>{{rp|7&ndash;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|append-only]] (sequential) zones of overlapping tracks that need to be rewritten entirely when full, resembling flash blocks in [[Solid-state drive|solid-state drive]]s. ''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.<ref name="snia-smr" />{{rp|11 ff.}}<ref>{{cite web |url=https://lwn.net/Articles/591782/ |title=Support for shingled magnetic recording devices |author=Jake Edge |publisher=LWN.net |date=March 26, 2014 |accessdate=December 14, 2014}}</ref> While SMR drives can use [[Dynamic random-access memory|DRAM]], [[Flash memory|flash memory]], and even a portion of their own [[Hard disk drive platter|platter]] reserved for use with CMR instead of SMR,<ref name="sthzfstest">{{Cite web |last=Taillac |first=Will |date=2020-05-28 |title=WD Red SMR vs CMR Tested Avoid Red SMR |url=https://www.servethehome.com/wd-red-smr-vs-cmr-tested-avoid-red-smr/ |access-date=2023-02-13 |website=ServeTheHome |language=en-US}}</ref> as a [[Cache (computing)|cache]] to improve writing performance, continuous writing of large amount of data is noticeably slower than with CMR drives.<ref>{{Cite web |title=The Evolution of HDDs in the Near Future: Speaking with Seagate CTO, Mark Re |url=https://www.anandtech.com/show/10470/the-evolution-of-hdds-in-the-near-future-speaking-with-seagate-cto-mark-re |last=Shilov |first=Anton |website=www.anandtech.com |access-date=2020-05-30}}</ref><ref name="Salter"/><ref name=Alcorn>{{cite news |last=Alcorn |first=Paul |title=Sneaky Marketing Redux: Toshiba, Seagate Shipping Slower SMR Drives Without Disclosure, Too |url=https://www.tomshardware.com/news/sneaky-marketing-toshiba-seagate-wd-smr-drives-without-disclosure |work=Tom’s Hardware |access-date=17 April 2020}}</ref>

==History==
[[Company:Seagate Technology|Seagate]] started shipping device-managed SMR hard drives in September 2013, stating an increase in overall capacity of about 25% compared to non-shingled storage.<ref name="anandtech-7290" /><ref>{{cite web |title=Seagate Delivers On Technology Milestone: First To Ship Hard Drives Using Next-Generation Shingled Magnetic Recording |url=https://www.seagate.com/news/news-archive/shingled-magnetic-recording-milestone-pr-master/ |website=www.seagate.com |access-date=28 October 2021 |date=9 September 2013}}</ref> In September 2014, [[Company:HGST|HGST]] announced a 10&nbsp;TB drive filled with [[Chemistry:Helium|helium]] that uses host-managed shingled magnetic recording,<ref>{{Cite news |title= Shingled platters breathe helium inside HGST's 10TB hard drive |author= Geoff Gasior |date= September 9, 2020|work= The Tech Report |url= http://techreport.com/news/27031/shingled-platters-breathe-helium-inside-hgst-10tb-hard-drive |accessdate=February 9, 2020}}</ref> although in December 2015 it followed this with a 10&nbsp;TB helium-filled drive that uses conventional non-shingled perpendicular recording.<ref>{{cite news |title=HGST releases helium-filled 10TB hard drive; Seagate twiddles shingled fingers |author=Sebastian Anthony |date=3 December 2020 |work=Ars Technica |url=http://arstechnica.co.uk/information-technology/2020/12/hgst-releases-helium-filled-10tb-hard-drive-seagate-twiddles-shingled-fingers/ |accessdate=3 December 2015}}</ref>

[[Company:Western Digital|Western Digital (WD)]], [[Company:Toshiba|Toshiba]], and [[Company:Seagate Technology|Seagate]] have sold SMR drives without labeling them as such, generating a large controversy, as SMR drives behave much slower under some circumstances (such as random writes) than CMR drives.<ref name=Salter>{{cite news |last=Salter |first=Jim |title=Sneaky Marketing Redux: Toshiba, Seagate Shipping Slower SMR Drives Without Disclosure, Too |url=https://arstechnica.com/gadgets/2020/04/caveat-emptor-smr-disks-are-being-submarined-into-unexpected-channels/ |work=Ars Technica |access-date=17 June 2020}}</ref> Some have even claimed that these may cause data loss.<ref name="ixblog">{{Cite web |last=Team |first=iX |date=2020-06-29 |title=WD Red Plus drives are "Coke Classic" |url=https://www.truenas.com/blog/wd-red-plus-drives/ |access-date=2023-09-24 |website=TrueNAS - Welcome to the Open Storage Era |language=en-US}}</ref> These mislabeling practices were used in both consumer-centric and dedicated data storage HDDs for servers, [[Network-attached storage|NASes]], RAIDs, and [[Cold data|cold storage]]. A United States class-action suit against Western Digital alleging that the technology is inferior was settled on or before August&nbsp;27, 2021.<ref>{{cite web |url=https://topclassactions.com/lawsuit-settlements/consumer-products/electronics/1030245-western-digital-hard-drive-2-7m-class-action-settlement/ |website=Top Class Actions |access-date=24 November 2021 |title= Western Digital Hard Drive $2.7M Class Action Settlement |archive-url= https://web.archive.org/web/20211124152833/https://topclassactions.com/lawsuit-settlements/consumer-products/electronics/1030245-western-digital-hard-drive-2-7m-class-action-settlement/ |archive-date=24 November 2021 }}</ref> Due to the controversy Western Digital now, as of June 2020, labels their DM-SMR NAS drives as "WD Red" and brands their CMR NAS drives as "WD Red Plus" and "WD Red Pro".<ref>{{Cite web |last=S |first=Ganesh T. |title=Western Digital Announces Red Plus HDDs, Cleans Up Red SMR Mess with Plus Branding |url=https://www.anandtech.com/show/15878/western-digital-cleans-up-the-red-smr-nas-hdd-mess |access-date=2023-09-24 |website=www.anandtech.com}}</ref><ref name="ixblog"/>

Heavily overlapped (shingled) tracks also appeared earlier in the consumer [[Engineering:Helical scan|helical scan]] video cassette recorders (VCRs) that were popular in the 1980s and 1990s. In Extended Play (EP or SLP) mode, both [[VHS]] and [[Betamax]] reduced the track pitch by a factor of three. The severe interference from the adjacent tracks was partially mitigated by the use of slant [[Engineering:Azimuth recording|azimuth recording]].

==Data management==
There are three different ways that data can be managed on an SMR drive: device-managed, host-managed and host-aware.<ref>{{cite web |url=http://www.t10.org/cgi-bin/ac.pl?t=f&f=zbc-r05.pdf |title=Zoned Block Commands (ZBC) |website=t10.org |publisher=ANSI T10 Committee |access-date=22 January 2018}}</ref><ref>{{cite web |url=http://www.snia.org/sites/default/files/SDC15_presentations/smr/JorgeCampello_SMR_Next_Generation_Storage_Technology.pdf |title=SMR: The Next Generation of Storage Technology |first=Jorge |last=Campello |date=24 September 2015 |access-date=22 January 2018}}</ref>

===Device-managed===
A ''device-managed'' or ''drive-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. Sequential writes are more efficient. In addition, the host is unaware that the storage is shingled.<ref name="snia-smr" />

The [[Engineering:Disk controller|disk controller]] in a device-managed drive internally handles any re-writing required by the special characteristics of a shingled drive, similar to the way a [[Flash memory controller|flash memory controller]] in a solid-state-drive internally handles re-writing required by the special characteristics of flash media.<ref name="ixcompat"/> SMR drives have [[Append-only|append-only]] zones which operate like SSD blocks, where a sector in a zone cannot be modified without re-writing the entire contents of the zone, so writes are first sent to a CMR cache and the disk moves these data to SMR parts when idle.<ref name="nonshingledzones"/>

Until backlash against Western Digital in 2020, this type of SMR drive was often not labelled by the manufacturer, except in disks labelled as "archival".<ref name="Salter"/><ref name=Alcorn/>

RAID resilvering tends to overload the cache,{{why|date=February 2021}} sending SMR drives into minutes-long pauses.{{fact|date=February 2021}} Faulty firmware (such as revision 82.00A82 on the WD40EFAX) may also cause the drive to return IDNF [[Engineering:Self-Monitoring, Analysis and Reporting Technology|S.M.A.R.T.]] errors under intensive workloads.<ref name="sthzfstest"/><ref name="ixcompat">{{Cite web |title=WD Red SMR Drive Compatibility with ZFS |url=https://www.truenas.com/hardware/notices/componentarticles/wdsmr/ |access-date=2023-09-24 |website=www.truenas.com |language=en}}</ref> Both behaviors tend to be interpreted as drive failure by the RAID controller.<ref name="nonshingledzones">{{cite web |last1=Mellor |first1=Chris |title=Shingled hard drives have non-shingled zones for caching writes |url=https://blocksandfiles.com/2020/04/15/shingled-drives-have-non-shingled-zones-for-caching-writes/ |website=Blocks and Files |date=15 April 2020}}</ref>

The zoned nature of SMR also means that the disk suffers from [[Engineering:Write amplification|write amplification]] when [[Garbage collection (computer science)|garbage collecting]],<ref name=fast16>{{cite journal |last1=Brewer |first1=Eric |last2=Ying |first2=Lawrence |last3=Greenfield |first3=Lawrence |last4=Cypher |first4=Robert |last5=T'so |first5=Theodore |title=Disks for Data Centers |journal=Proceedings of USENIX FAST 2016 |date=2016 |url=https://research.google/pubs/pub44830/ |language=en}}</ref> although for hard drives the main problem with writes is speed instead of longevity. Some SMR hard drives support the [[Engineering:Trim (computing)|TRIM]] command for this reason.<ref>{{cite web |title=TRIM Command Support for WD External Drives |url=https://support-en.wd.com/app/answers/detail/a_id/25185 |website=WD support}}</ref>

===Host-managed===
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.<ref name="snia-smr" />

===Host-aware===
''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.<ref name="snia-smr" />

== Protocol ==
SMR devices are considered ''zoned'' devices, as the storage is divided into zones of usually 256&nbsp;MiB size.<ref name=zonectl/> Two sets of specialized commands, ZBC (Zoned Block Commands, ANSI INCITS 536) for [[Engineering:SCSI|SCSI]] and ZAC (Zoned ATA Commands, ANSI INCITS 537) for [[Engineering:SATA|SATA]] are available for SMR devices. They tell the host about whether each zone is CMR or SMR and allow them to address these zones directly.<ref name="tom">{{Cite web|archive-url=https://web.archive.org/web/20170611164138/http://www.tomsitpro.com/articles/shingled-magnetic-recoding-smr-101-basics,2-933.html|archive-date=2017-06-11|url=http://www.tomsitpro.com/articles/shingled-magnetic-recoding-smr-101-basics,2-933.html|title=SMR (Shingled Magnetic Recording) 101|accessdate=2018-03-03|publisher=Tom's IT Pro|language=en}}</ref> Unless specifically mentioned, the commands are only available on host-aware/-managed devices. The specific commands are:<ref>{{cite web |title=Introduction to Shingled Magnetic Recording |url=https://zonedstorage.io/introduction/smr/ |website=ZonedStorage.io}}</ref>

* REPORT ZONES, for information on disk layout and zone status (such as the ''write pointer'', the last-written position in a sequential zone)
** SMR or similar zones are ''sequential required'' on host-managed drives, but ''sequential preferred'' on host-aware ones.
* RESET WRITE POINTER, for rewinding the write pointer so a sequential zone becomes empty
* OPEN ZONE, for explicitly declaring access to a zone and locking the associated firmware resources
* CLOSE ZONE, to unlock an opened zone
* FINISH ZONE, fill a zone full and make it readable

Each zone has a range of [[Logical block addressing|LBA]] addresses associated with it, and all LBA-based commands can be used as long as the sequential requirement is followed on host-managed drives.

SMR devices identify themselves per the following:<ref>{{cite web |title=Information technology - ATA Command Set - 4 (ACS-4), Draft revision 18 |url=http://t13.org/Documents/UploadedDocuments/docs2017/di529r18-ATAATAPI_Command_Set_-_4.pdf}}</ref><ref>{{cite web |last1=Seagate |title=SCSI Commands Reference Manual, Rev. J |url=https://www.seagate.com/files/staticfiles/support/docs/manual/Interface%20manuals/100293068j.pdf |page=472}}</ref><ref name="snia-smr"/>{{rp|14}}

* Host-aware or device-managed drives are marked as normal block devices ([[Engineering:SCSI Peripheral Device Type|SCSI]] 00h), so they can be recognized as a normal hard drive.
** A ZONED field shows whether the drive is device-managed, host-aware, or neither. This is found in the SCSI Block Device Characteristics VPD page and the ATA capabilities log page.
* Host-managed drives use a new device type (SCSI 14h). Only ZAC/ZBC-aware computers can detect and use them.

A newer version of the sibling standards, ZAC-2/ZBC-2 is under development. The new version introduces a new type of "domains and realms zoned block devices" that allow for non-contiguous LBAs.<ref>T10, 2020.</ref> The ZONED field has been retired following a proposal from [[Company:Western Digital|Western Digital]].<ref>{{cite web |last1=Weber |first1=Ralph O |date=April 23, 2020 |title=SBC-5, ZBC-2: Obsolete the ZONED field |url=https://www.t10.org/cgi-bin/ac.pl?t=d&f=20-054r1.pdf |website=www.t10.org |url-access=registration}}</ref>

The zoned interface is also useful for flash storage. ZNS spec has been released by the [[Engineering:NVM Express|NVM Express]] organization.<ref>{{cite web |title=NVMe Command Set Specifications|date=January 10, 2020 |url=https://nvmexpress.org/developers/nvme-command-set-specifications/ }}</ref>

== Software and application ==
The higher density of SMR drives, combined with its random-read nature, fills a niche between the sequential-access tape storage and the random-access conventional hard drive storage. They are suited to storing data that are unlikely to be modified, but need to be read from any point efficiently. One example of the use case is [[Software:Dropbox (service)|Dropbox]]'s ''Magic Storage'' system, which runs the on-disk ''extents'' in an append-only way.<ref name=dbsmr>{{Cite web|url=https://dropbox.tech/infrastructure/extending-magic-pocket-innovation-with-the-first-petabyte-scale-smr-drive-deployment|title=Extending Magic Pocket Innovation with the first petabyte scale SMR drive deployment|author=Magic Pocket Hardware Engineering Teams|website=dropbox.tech}}</ref> Device-managed SMR disks have also been marketed as "Archive HDDs" due to this property.<ref>{{Cite web|url=https://www.seagate.com/www-content/product-content/hdd-fam/seagate-archive-hdd/en-us/docs/archive-hdd-ds1834-5c-1508us.pdf|title=Archive HDD|publisher=Seagate|accessdate=2019-03-03|language=en}}</ref>

A number of [[File system|file system]]s in [[Software:Linux|Linux]] are or can be tuned for SMR drives:<ref>{{cite web |title=File Systems|url=https://zonedstorage.io/linux/fs/ |website=ZonedStorage.io}}</ref>

* [[F2FS]], originally designed for flash media, has a Zoned Block Device (ZBD) mode. It can be used on host-managed drives with conventional zones for metadata. 
* [[Btrfs]] had ZBD support added in Linux kernel 5.12, and it already writes mostly sequentially due to the CoW nature.
* [[Ext4|ext4]] can be experimentally tuned to write more sequentially. Theodore Ts'o and Abutalib Aghayev gave a talk in 2017 on their ''ext4-lazy''. Seagate also has a more radical "SMRFFS" extension from 2015 that makes use of the ZBC/ZAC commands.<ref>{{cite web |title=Seagate/SMR_FS-EXT4: an addition to the popular EXT4 to enable support for devices that use the ZBC or ZAC standards |url=https://github.com/Seagate/SMR_FS-EXT4 |publisher=Seagate Technology |date=10 December 2019}}</ref>
* For other filesystems, the Linux device mapper has a ''dm-zoned'' target that maps a host-managed drive into a random-writable drive. Linux kernels since 4.10 can perform this task without ''dm''.<ref>{{cite web |title=Device Mapper |url=https://zonedstorage.io/linux/dm |website=ZonedStorage.io}}</ref> A ''{{Not a typo|zonefs}}'' from 2019 exposes the zones as files for easier access.<ref>{{cite web |last1=Le Moal |first1=Damien |title=fs: New zonefs file system |url=https://lwn.net/Articles/793585/ |website=lwn.net}}</ref>

In addition to Linux, [[Software:FreeBSD|FreeBSD]] has protocol-level support for host-managed SMR drives.<ref name=zonectl>{{man|8|zonectl|FreeBSD}}</ref><ref>{{cite web | url = https://svnweb.freebsd.org/base?view=revision&revision=300207 | title = FreeBSD Revision 300207: Add support for managing Shingled Magnetic Recording (SMR) drives. | date = 2015-05-19 | first = Kenneth | last = Merry }}</ref> {{As of|2020|04}}, neither Windows nor MacOS supports the ZBC/ZAC commands required for such drives to work.{{cn|date=October 2023}}

===Dynamic hybrid SMR===
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.<ref>{{cite web|url=https://blog.westerndigital.com/dynamic-hybrid-smr/|title=Dynamic Hybrid SMR|last=Collins|first=Brendan|date=13 November 2017|publisher=Western Digital|accessdate=25 August 2018}}</ref><ref>{{cite web|url=https://www.blog.google/topics/google-cloud/dynamic-hybrid-smr-ocp-proposal-improve-data-center-disk-drives/|title=Dynamic Hybrid-SMR: an OCP proposal to improve data center disk drives|date=13 November 2017|website=blog.google|access-date=22 January 2018}}</ref> Adjusting the SMR/CMR setting helps suit the drive to the current workload of "hot" and "cold" data.<ref name=fast16/>

== Criticism ==
SMR drives have received criticism online for slow read and write speeds.<ref>{{Cite web |title= |url=https://www.tenforums.com/performance-maintenance/106725-very-slow-boot-time-100-disk-active-time-post2019066.html#post2019066}}</ref><ref>{{Cite web |last=Illeazar |date=2020-08-03 |title=I knew SMR had slow write speeds, but 1MB/second? |url=http://www.reddit.com/r/DataHoarder/comments/i2zmum/i_knew_smr_had_slow_write_speeds_but_1mbsecond/ |access-date=2024-01-29 |website=r/DataHoarder}}</ref><ref>{{Cite web |last=NeaZerros |date=2021-06-22 |title=Slow read speeds on SMR drives |url=http://www.reddit.com/r/DataHoarder/comments/o5l0mk/slow_read_speeds_on_smr_drives/ |access-date=2024-01-29 |website=r/DataHoarder}}</ref><ref>{{Cite web |last=vanderworp |date=2023-01-17 |title=SMR hard disks: Avoid them! |url=https://vanderworp.org/smr-hard-disks-avoid-them/ |access-date=2024-01-29 |website=vanderworp.org |language=en-GB}}</ref><ref>{{Cite web |last=Taillac |first=Will |date=2020-05-28 |title=WD Red SMR vs CMR Tested Avoid Red SMR |url=https://www.servethehome.com/wd-red-smr-vs-cmr-tested-avoid-red-smr/ |access-date=2024-01-30 |website=ServeTheHome |language=en-US}}</ref> Drive manufacturers have been further criticised for attempting to conceal the use of SMR technology in their products.<ref>{{Cite web |last=Mellor |first=Chris |date=2020-04-15 |title=Seagate 'submarines' SMR into 3 Barracuda drives and a Desktop HDD |url=https://blocksandfiles.com/2020/04/15/seagate-2-4-and-8tb-barracuda-and-desktop-hdd-smr/ |access-date=2024-01-30 |website=Blocks and Files |language=en-US}}</ref><ref>{{Cite web |last=updated |first=Paul Alcorn last |date=2020-04-14 |title=Western Digital Fesses Up: Some Red HDDs Use Slow SMR Tech Without Disclosure |url=https://www.tomshardware.com/news/wd-fesses-up-some-red-hdds-use-slow-smr-tech |access-date=2024-01-30 |website=Tom's Hardware |language=en}}</ref>

== See also ==
* Heat-assisted magnetic recording (HAMR)
* [[Log-structured file system]], a type of file system optimized for append-only media
* [[Engineering:Patterned media|Patterned media]]
* [[Engineering:Two-dimensional magnetic recording|Two-dimensional magnetic recording]]

== References ==
{{Reflist|30em}}

== External links ==
* [https://lwn.net/Articles/548116/ LSFMM: A storage technology update], LWN.net, April 23, 2013, by Jonathan Corbet
* [https://events.static.linuxfound.org/sites/events/files/slides/SMR-LinuxConUSA-2014.pdf SMR Impact on Linux Storage Subsystem], HGST, 2014, by Jorge Campello and Adam Manzanares
* [http://xfs.org/images/f/f6/Xfs-smr-structure-0.2.pdf Layout optimisation for using XFS on host-managed SMR drives], March 2015
* [https://events.static.linuxfound.org/sites/events/files/slides/SMR%20in%20Linux%20Systems%20-%20Vault.pdf SMR in Linux Systems], Seagate, March 18, 2015, by Adrian Palmer
* [http://open-zfs.org/w/images/2/2a/Host-Aware_SMR-Tim_Feldman.pdf Host-Aware SMR], Seagate, November 10, 2014, by Timothy Feldman
* [https://www.snia.org/sites/default/files/files2/files2/SDC2013/presentations/Hardware/AlbertChenMalina_Addressing_Shingled_Magnetic_Recording.pdf Addressing Shingled Magnetic Recording drives with Linear Tape File System], SNIA SDC 2013, by Albert Chen and Jim Malina
* [https://www.snia.org/sites/default/files/SDC15_presentations/smr/AlbertChen_JimMalina_Host_Managed_SMR_revision5.pdf Host Managed SMR], SNIA SDC 2015, by Albert Chen, Jim Malina and TK Kato

=== Specifications ===
* ZAC/ZBC version 1 (published 2016)
** T10, [https://www.t10.org/ftp/zbcr01.pdf Information technology - Zoned Block Commands (ZBC)], 2014, Draft revision 1
** T13, [http://www.t13.org/Documents/UploadedDocuments/docs2015/di537r05-Zoned_Device_ATA_Command_Set_ZAC.pdf Information technology - Zoned Device ATA Command Set (ZAC)], Draft revision 5, 2015
* ZAC/ZBC version 2 (under development as of 2020){{anchor|zbc2-spec}}
** T10, [https://www.t10.org/cgi-bin/ac.pl?t=f&f=zbc2r04a.pdf Information technology - Zoned Block Commands - 2 (ZBC-2)], 2020, Draft revision 04a
** T13, ZAC-2, PDF unavailable

[[Category:Computer storage technologies]]
[[Category:Hard disk drives]]

{{Sourceattribution|Shingled magnetic recording|1}}