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Shingled magnetic recording

Shingled magnetic recording (SMR) is a hard disk drive (HDD) technology designed to increase areal density by writing data tracks that partially overlap adjacent tracks, resembling the overlapping arrangement of shingles on a roof.^[1] This method employs a wider write head to overlap track edges while using a narrower read head to retrieve data precisely, thereby overcoming limitations in scaling track widths for conventional perpendicular magnetic recording (PMR).^[2] Data is organized into logical bands or zones to manage overlaps, enabling sequential writes that boost storage efficiency without requiring major changes to existing HDD architectures.^[3] The primary advantage of SMR lies in its capacity to enhance areal density by 10-25% per platter compared to non-overlapping PMR drives, enabling HDDs with capacities up to 32 TB and beyond as of 2025 and reducing the cost per gigabyte of storage.^[4]^[2]^[5] By maintaining strong magnetic write fields through wider heads, SMR addresses the challenges of narrowing tracks in traditional recording, supporting sustained growth in data storage demands for cloud, archival, and enterprise applications.^[3] It also improves reliability by potentially using fewer heads and platters in higher-capacity designs.^[4] A key challenge with SMR is the inability to perform efficient random writes or in-place updates, as overwriting one track destroys data in overlapping adjacent tracks, often requiring the entire band to be read, modified, and rewritten.^[1] To address this, SMR implementations incorporate management techniques such as drive-managed systems (which handle sharding, over-provisioning, and garbage collection internally), host-managed approaches (where the operating system or application sequences writes), and cooperative models that share responsibilities between drive and host.^[1]^[6] These strategies make SMR suitable for sequential workloads like backups and big data analytics but may introduce latency for random-access patterns without optimization.^[6] SMR technology emerged in the late 2000s as a bridge to extend the viability of magnetic recording beyond PMR limits, with Seagate becoming the first to commercially ship SMR-based drives in 2013, initially targeting capacities up to 5 TB.^[4] By the mid-2010s, it was integrated with advancements like two-dimensional magnetic recording (TDMR) to further mitigate inter-track interference during reads.^[2] As of 2025, SMR is widely adopted in high-capacity enterprise and nearline HDDs from major manufacturers, contributing to exabyte-scale data centers, with commercial integration of heat-assisted magnetic recording (HAMR) enabling capacities up to 30 TB while hybrid systems combining SMR with SSD caching provide balanced performance.^[3]^[6]^[7]

Overview

Principles of Operation

Shingled magnetic recording (SMR) is a hard disk drive technology that increases areal density by writing successive data tracks such that they partially overlap, resembling the layout of shingles on a roof. This approach allows tracks to be narrower than in conventional recording while using existing perpendicular magnetic recording (PMR) media and heads, enabling up to a 25% increase in storage capacity without major manufacturing changes.^[8] In SMR, the write head is wider than the read head, producing a magnetic field that overlaps the previous track by 50-90% of its width during sequential writes, thereby squeezing more tracks into the same radial space. The narrower read head can then access the non-overlapped portion of each track without interference from adjacent data, preserving read performance comparable to PMR. This geometry trades random write capability for density, as overwriting a track would corrupt downstream overlaps, necessitating sequential append-only operations.^[9] To manage overlaps, the disk surface is divided into fixed-size zones, typically 256 MiB bands of consecutive tracks treated as append-only sequences. Within a zone, logical block addressing supports sequential writes starting from a write pointer at the zone's beginning, filling the zone contiguously until full; reuse requires a zone reset or trim operation to relocate data and reclaim space. These zones prevent widespread data corruption from random updates by confining shingling effects.^[10]^[9] Compared to conventional PMR, where tracks are written non-overlapping with equal-width read and write heads, SMR achieves higher areal density through overlap but requires adapted data placement to avoid read-modify-write cycles for updates. This results in density gains of 20-30% in practical implementations, extending the scalability of magnetic recording beyond PMR limits.^[11]^[12]

Advantages and Challenges

Shingled magnetic recording (SMR) enables significant increases in areal density by overlapping adjacent tracks, allowing for up to 25% higher storage capacity compared to conventional perpendicular magnetic recording (PMR) drives of similar physical size.^[1] This density advantage has driven SMR adoption in high-capacity hard disk drives, with commercial products reaching 32 TB as of 2024, supporting transitions from earlier 10 TB PMR models to meet growing data demands.^[13] Consequently, SMR reduces the cost per terabyte, offering approximately 20% savings in total cost of ownership for hyperscale storage systems through efficient use of existing manufacturing processes.^[14] In data centers, SMR's higher density minimizes the number of drives required for equivalent storage volumes, leading to lower material consumption and improved energy efficiency by reducing overall power draw and cooling needs.^[15] This scalability supports exabyte-scale deployments for cloud computing and archival storage, where sequential workloads predominate, and the global SMR market is projected to grow from $4.15 billion in 2024 to $8.3 billion by 2033 at a compound annual growth rate of 8.4%.^[16] Such benefits position SMR as a cost-effective solution for sustainable data growth in energy-constrained environments.^[17] Despite these gains, SMR introduces write amplification, where updating data in a zone necessitates reading, modifying, and rewriting the entire zone—often shifting downstream data—to avoid corrupting overlapping tracks.^[1] This process can amplify write operations by factors proportional to zone size, exacerbating latency in random write scenarios. Random write performance in SMR drives is significantly slower than in PMR equivalents, with sustained speeds dropping to 40 MB/s or less after cache exhaustion, compared to 80–160 MB/s for PMR, potentially up to 4–10 times slower in worst-case zone management.^[12]^[18] Read performance remains generally comparable to PMR drives, as the shingled geometry imposes minimal constraints on retrieval, though occasional latency arises from zone-level data management and potential fragmentation during heavy write activity.^[19] These trade-offs highlight SMR's suitability for write-once or sequential-access applications while necessitating careful workload alignment to mitigate operational bottlenecks.^[20]

History

Early Research and Development

Shingled magnetic recording (SMR) was proposed in the late 2000s as a technique to extend the areal density limits of perpendicular magnetic recording (PMR) by allowing tracks to overlap like shingles on a roof, thereby addressing the superparamagnetic trilemma of signal-to-noise ratio, thermal stability, and writability without requiring major changes to existing media or heads.^[21] The concept was introduced by researchers at Hitachi Global Storage Technologies (HGST), with the seminal paper "The Feasibility of Magnetic Recording at 10 Terabits Per Square Inch on Conventional Media" published in February 2009 by Roger Wood and colleagues, demonstrating that shingled writing combined with two-dimensional signal processing could achieve densities up to 10 Tb/in² on conventional granular media.^[21] This approach aimed to sidestep the narrowing write head constraints in PMR by using wider heads for sequential writes, enabling higher track densities while maintaining readability through advanced readback methods.^[21] Research on SMR accelerated from around 2008, with laboratory prototypes developed between 2009 and 2012 showcasing areal density gains of 20-30% over conventional PMR drives through overlapping track geometries.^[10] Key milestones included HGST's 2010 spinstand demonstrations of shingled write/read operations achieving over 800 Gb/in² in controlled settings, alongside contributions from IBM researchers and academic collaborations on head designs and signal processing algorithms.^[10] These efforts involved institutions like the University of Manchester, which co-authored foundational simulations showing viable error rates at high densities.^[21] Early laboratory work focused on mitigating challenges from overlapping tracks, such as inter-track interference and the need for sequential access, through the development of banding algorithms to group tracks into rewrite units and enhanced error correction codes tailored for shingled geometries.^[10] HGST and Seagate filed initial patents in 2010 addressing these issues; for instance, HGST's US Patent 8,537,481 (filed August 2011, priority 2010) described methods to minimize far-track erasure in shingled bands, while Seagate's US Patent 8,896,961 (filed April 2010) covered reader positioning for overlapping tracks.^[22]^[23] By 2011, the transition to potential commercialization prompted early discussions within the INCITS T10 committee on zoned storage interfaces to support SMR's sequential-write semantics, laying the groundwork for the Zoned Block Commands (ZBC) standard.^[24] These efforts emphasized device-level management of zones to handle the non-overwritable nature of shingled tracks, influencing subsequent host-aware implementations.^[10]

Commercial Introduction and Adoption

The commercial introduction of shingled magnetic recording (SMR) technology marked a significant milestone in hard disk drive (HDD) development, beginning with Seagate's announcement in September 2013 of the first drives utilizing SMR to achieve up to a 25% increase in areal density, enabling capacities such as 2-4 TB in the Archive HDD series for nearline storage applications.^[4] These initial products targeted cost-sensitive, sequential-write workloads like archiving, providing a practical boost in capacity without immediate widespread disruption to conventional perpendicular magnetic recording (PMR) designs. Following closely, HGST (now part of Western Digital) launched the Ultrastar Archive Ha10, the industry's first enterprise-class 10 TB helium-filled SMR drive for archive storage, in June 2015, leveraging seven platters to set a new benchmark for high-capacity, low-power storage in cool/cold environments.^[25]^[26] Early adoption faced hurdles, notably a 2021 class-action lawsuit against Western Digital alleging undisclosed SMR implementation in WD Red NAS drives, which resulted in a $2.7 million settlement and prompted industry-wide improvements in drive labeling and transparency standards to address compatibility issues in RAID and random-write scenarios.^[27] By the early 2020s, SMR gained traction in specialized sectors, evolving from niche archive use to broader integration in enterprise storage. Toshiba also introduced SMR drives in the mid-2010s, contributing to diversified adoption across manufacturers. Recent advancements as of 2025 underscore SMR's maturation, with Toshiba introducing a 24 TB SMR model in the S300 series for video surveillance applications on November 5, 2025, doubling prior capacities in this segment to support AI-driven analytics and continuous recording.^[28] Seagate has advanced toward 40 TB HAMR drives using SMR, with engineering samples shipped in 2025 for data center qualification, combining heat-assisted magnetic recording with shingled enhancements for hyperscale demands, though full production is slated for 2026.^[29] Market projections indicate robust growth, with the SMR sector expected to expand from $1.65 billion in 2024 to approximately $7.33 billion by 2032 at a 20.5% CAGR, driven by capacity needs in exabyte-scale environments.^[30] Adoption trends reflect increasing acceptance, particularly in cloud storage where hyperscalers such as AWS, Google, and Meta have incorporated SMR drives by 2024 to achieve about 20% higher capacity per unit compared to conventional HDDs, optimizing costs for archival and sequential workloads.^[30] In surveillance and enterprise settings, SMR elements now feature in a growing share of new HDDs amid surging data from AI and video analytics.^[31]

Technical Fundamentals

Track Geometry and Zoning

In shingled magnetic recording (SMR), the track geometry is designed to exploit the difference between write and read head widths to achieve higher areal density. The write head is significantly wider than the read head, typically around twice as wide, allowing new tracks to overlap previously written ones while the narrower read head can still access the residual data in the non-overlapped portion of the older track. For example, early conceptual designs featured a write track width of approximately 70 nm compared to a conventional read track width of 25 nm, enabling overlaps that reduce the effective track pitch and yield a density multiplier of 1.3 to 1.5 times over perpendicular magnetic recording (PMR) in models, though commercial implementations typically achieve 10-25% gains.^[32] This geometry inherently introduces adjacent track interference (ATI), where the magnetic fields from overlapping writes can degrade neighboring tracks, but it is mitigated through precise head positioning and signal processing techniques.^[33] SMR drives organize tracks into zones, which serve as sequential write namespaces to manage the overwrite constraints imposed by shingling. A typical SMR drive is divided into thousands of such zones—for instance, a multi-terabyte drive might contain over 30,000 zones—each functioning as a contiguous block where data must be written sequentially from the inner to outer edges to avoid disturbing prior data. Each zone commonly holds around 500 tracks, though this varies with drive capacity and geometry, ensuring that random overwrites are prevented by treating the zone as an append-only structure until it is reset.^[34] Zones are separated by guard bands of non-shingled tracks to isolate interference and allow independent management.^[32] Banding variations in SMR include fixed-band and variable-band configurations, adapting to different management needs. Fixed-band SMR uses uniform zone sizes across the drive, such as 256 MiB per zone, which simplifies firmware handling in device-managed implementations but may lead to internal fragmentation in zones with varying track densities due to the drive's zoned geometry. Variable-band SMR, in contrast, allows flexible zone capacities ranging from 32 MiB to 512 MiB, accommodating host-aware or host-managed schemes where zone boundaries can align with application workloads for better efficiency.^[34] As of 2024, modern commercial drives, like those from Western Digital and Seagate, predominantly employ fixed-band zoning with 256 MiB zones to standardize compliance with protocols like Zoned Block Commands (ZBC).^[33] Error management in SMR track geometry incorporates built-in redundancy to counter ATI, with shingled-specific error correction codes (ECC) enhancing reliability. Stronger ECC schemes, such as low-density parity-check (LDPC) codes tailored for two-dimensional interference, are applied across multiple adjacent tracks during reads to correct errors from partial overlaps without frequent rewrites. This redundancy adds a small overhead but ensures bit error rates remain below 10^{-15}, critical for enterprise applications, by integrating inter-track parity and iterative decoding algorithms.^[35]

Read and Write Mechanisms

In shingled magnetic recording (SMR), the write process relies on sequential appending of data tracks within defined zones, where each new track partially overlaps the previous one to maximize areal density. This is achieved using a write head wider than the target track width, typically offset to overlap only the trailing edge of the prior track in a one-directional manner, eliminating inter-track gaps and allowing track pitches as narrow as 10-20 nm. Overwriting an individual track is not possible without corrupting adjacent data; instead, it necessitates a read-modify-write operation that rewrites the entire affected zone, resulting in write amplification factors scaling with zone size (often hundreds of tracks), typically leading to 100x or more for random single-track updates in commercial drives.^[32]^[10]^[36] The read process in SMR is non-destructive and supports random access, leveraging narrower read heads (e.g., 10-20 nm width) that can isolate the readable portion of a shingled track despite overlaps from adjacent writes. These heads exploit the asymmetry between writing and reading capabilities, where reading thin tracks is feasible even if writing them directly is challenging due to magnetic field requirements. While random reads are viable, sequential reads are preferred for efficiency, as they minimize head seeks and reduce inter-track interference effects, potentially mitigated further by techniques like two-dimensional magnetic recording (TDMR) using multiple offset read elements.^[32]^[36] Head technology in SMR distinguishes between one-sided shingled writing, the predominant approach where overlaps occur unidirectionally, and experimental two-sided variants that enable shingling on both edges for potentially higher densities but increased complexity in track management. Seagate's implementations, for instance, primarily use one-sided writing with optimized head designs, yielding areal density gains of 7-15% over conventional perpendicular recording in capacities around 24 TB as of 2023. To isolate zones and accommodate active rewriting without spillover, buffer zones—implemented as guard bands or dedicated unshingled rewrite areas—separate shingled regions, typically accounting for 1-5% of total drive capacity.^[32]^[37]

Data Management Approaches

Device-Managed SMR

Device-managed shingled magnetic recording (SMR), also referred to as drive-managed SMR, is an implementation where the hard disk drive's firmware internally manages the sequential-write constraints and data shingling process to emulate the behavior of a conventional perpendicular magnetic recording (PMR) drive. This approach provides full backward compatibility with existing host systems and applications, as the drive exposes a standard block device interface without requiring any modifications to host software or operating systems. The firmware handles zone management, data rewriting, and track overlapping transparently, absorbing the complexities of SMR to maintain random read and write accessibility from the host's perspective.^[36]^[34] In terms of implementation, device-managed SMR relies on a shingled translation layer within the drive firmware to map logical block addresses to physical shingled tracks, often utilizing an on-drive cache composed of conventional (non-shingled) CMR regions to buffer random writes and mitigate write amplification. For instance, Seagate's early device-managed SMR drives, such as the 8 TB Archive HDD, incorporate an "E-region" persistent cache equivalent to about 1% of the drive capacity (approximately 80 GB), alongside a 128 MB DRAM buffer for immediate write buffering and zone mapping. This setup allows the drive to handle write amplification factors up to 10 times higher than PMR drives during intense random workloads by rewriting affected shingled bands in the background, without exposing these operations to the host.^[34]^[38] Performance in device-managed SMR drives closely mirrors that of PMR drives for sequential reads and writes when operating within the cache capacity, achieving sustained throughput rates comparable to conventional HDDs, such as around 150-200 MB/s for sequential operations. However, under heavy random I/O workloads that exceed the cache limits, performance can degrade due to internal band rewrites and garbage collection, resulting in sustained write speeds dropping to 100-200 MB/s or lower, depending on drive utilization and firmware efficiency. Advanced firmware schemes, like the track-based translation layer proposed in research, can reduce write amplification to as low as 0-6% in optimized scenarios, helping maintain near-PMR performance up to 90% drive fill levels.^[34] Examples of device-managed SMR drives include Seagate's Archive HDD series, which began shipping in 2013 with capacities up to 8 TB, designed for archival and enterprise nearline storage without necessitating host-side changes.^[34]

Host-Managed SMR

Host-managed shingled magnetic recording (SMR) refers to an implementation where the host operating system or application directly controls the management of data zones on the drive, issuing specialized zoned commands to append data sequentially to zones and explicitly resetting zones as needed, without any drive-level mechanisms to conceal the effects of track shingling. This approach shifts the responsibility for ensuring data integrity and sequential write constraints entirely to the host, allowing the drive to expose its internal zone structure transparently via standards such as Zoned Block Commands (ZBC) for SCSI or Zoned ATA Commands (ZAC) for SATA interfaces. Unlike other SMR variants, host-managed drives reject non-sequential writes to zones, enforcing strict append-only behavior to maintain performance and avoid internal garbage collection delays.^[1]^[39] In typical workflows, applications interact with the drive as a zoned namespace (ZNS), querying zone states and capacities before appending data streams to open zones, which are fixed-size regions (often 256 MB) optimized for sequential filling. For instance, in archival backup or write-once storage scenarios like cloud object storage, the host sequentially fills zones with immutable data, minimizing overwrites and leveraging the drive's full areal density potential without random access interruptions. When a zone becomes full, the host must reset it—effectively erasing and preparing it for reuse—before appending new data, often coordinating this across multiple drives in distributed systems. Real-world deployments, such as Dropbox's exabyte-scale adoption of 14 TB host-managed SMR drives, demonstrate this by aligning data chunks sequentially within zones to support predictable ingestion of large, append-heavy workloads. Examples also include Western Digital's Ultrastar Archive Ha10 (10 TB, introduced 2015) and Ultrastar DC HC650 (20 TB, as of 2023), designed for enterprise nearline storage with host optimization.^[40]^[41]^[42]^[43]^[44] The primary benefits of host-managed SMR include enhanced sustained write performance for sequential workloads, potentially achieving up to twice the throughput of conventional perpendicular magnetic recording (PMR) drives in optimized setups, with examples reaching 200–250 MB/s for large sequential appends due to the elimination of drive-side buffering and cleaning overheads. This leads to lower total cost of ownership through higher capacity per drive (e.g., up to 30% density gains) and reduced power consumption in data centers. However, it demands zoned-aware software stacks; Linux kernel support for zoned block devices, usable with ext4 via the dm-zoned device mapper for sequential emulation, was introduced in version 4.10 (2017), enabling compatibility for host-managed drives in environments like archival storage.^[39]^[12]^[45] Limitations arise in workloads requiring frequent updates, as host-managed SMR performs poorly with random overwrites—common in databases—since filling a zone necessitates host-orchestrated resets and full rewrites, potentially causing latency spikes and inefficiency. Without application-level awareness, attempts at in-zone updates can lead to zone exhaustion and forced migrations, amplifying overhead compared to transparent drive-managed alternatives. Thus, it excels in append-dominant use cases but requires custom software adaptations to avoid performance pitfalls.^[1]^[42]

Host-Aware SMR

Host-Aware Shingled Magnetic Recording (HA-SMR) represents a hybrid data management model in which the drive exposes key zoning information, such as zone types, write pointers, and status (e.g., empty or full), to the host through standardized queries like the REPORT ZONES command, enabling collaborative optimization while the drive internally manages buffering for non-sequential operations.^[39]^[46] This approach builds on the Zoned Block Commands (ZBC) and Zoned ATA Commands (ZAC) standards, allowing the host to direct sequential writes to appropriate zones for efficiency, while the drive redirects random writes to a media cache and performs background migration and cleaning to maintain performance. Unlike fully host-managed systems, HA-SMR provides backward compatibility with conventional interfaces, making it suitable for gradual adoption in existing storage ecosystems.^[46] Implementation of HA-SMR typically supports a limited number of open zones—up to 128 sequential and 8-16 for random writes—beyond which sequential write throughput can degrade by approximately 57% due to increased cleaning overhead.^[39] The drive combines device-managed caching for handling bursts of non-sequential I/O without immediate performance penalties, with host-provided hints to align writes and minimize rewrites.^[39] For instance, Seagate enterprise drives, including models evaluated in storage research, incorporate HA-SMR features with partial zone exposure, allowing hosts to query and reset write pointers via the RESET WRITE POINTER command for optimized zone lifecycle management.^[46] This integration often involves host-side indirection buffers, such as circular-log structures spanning multiple zones, to further enhance I/O predictability.^[39] HA-SMR excels in workloads with mixed sequential and bursty access patterns, such as archival storage or hierarchical systems where it serves as a cost-effective second tier, delivering performance comparable to perpendicular magnetic recording (PMR) drives under light random write loads due to effective caching.^[39] In scenarios involving irregular I/O, like data ingestion in analytics pipelines, the host's awareness of zone states reduces latency spikes from rewrites, though sustained random writes may still incur cleaning delays of 1-30 seconds per zone.^[39] Overall, optimized HA-SMR configurations can achieve higher and more predictable throughput than unoptimized device-managed SMR, making it viable for general-purpose enterprise applications.^[19] The concept of HA-SMR emerged around 2016 as a superset of drive-managed and host-managed models, formalized through the INCITS T10 ZBC and T13 ZAC standards released in 2015-2016 to standardize zoned storage interfaces.^[39]^[46] As of 2025, HA-SMR and related zoned SMR technologies, primarily host-managed variants, have gained traction in data centers for capacities exceeding 30 TB, where shingled recording contributes to higher areal densities in enterprise drives from vendors like Seagate and Western Digital, supporting the surge in AI and big data storage demands. Host-managed SMR dominates high-capacity deployments, with host-aware seeing use in hybrid scenarios.^[47]^[17]

Protocols and Standards

Zoned Block Commands

Zoned Block Commands (ZBC) and Zoned Device ATA Command Set (ZAC) provide the standardized protocol interfaces for host systems to interact with zoned storage devices, including those using shingled magnetic recording (SMR). The ZBC standard (INCITS 536-2016), developed by the T10 committee under INCITS, defines commands for SCSI-based zoned block devices, while the semantically equivalent ZAC standard (INCITS 537-2016), from the T13 committee, applies to ATA/SATA interfaces. These protocols ensure interoperability by specifying how hosts query zone layouts, manage write pointers, and perform sequential writes, with ZBC and ZAC being mandatory for host-managed SMR drives since their ratification in 2016.^[48] Central to these standards are commands for zone reporting and manipulation. The REPORT ZONES command retrieves detailed information about all zones on the device, including their starting logical block addresses (LBAs), sizes, types (conventional or sequential-write required), and current states, allowing hosts to map the device's zoned geometry.^[24] The RESET WRITE POINTER command repositions the write pointer of one or more specified zones back to the zone's starting LBA, erasing prior data and enabling fresh sequential writes; this is essential for host-managed garbage collection and zone reuse.^[24] For efficient sequential writing, the Zone Append command (introduced in later revisions) allows data to be appended directly to a zone's current write pointer without the host needing to track the exact LBA, reducing overhead in append-only workloads. Zone management is handled through a set of commands that control zone activation and finalization. The OPEN ZONE command explicitly transitions an empty or closed sequential-write zone to an open state, allocating device resources for writing; CLOSE ZONE deactivates an open zone while preserving the write pointer for later resumption; and FINISH ZONE marks a zone as read-only, preventing further writes.^[49] These operations, along with RESET WRITE POINTER, form the core of zone lifecycle management. Zones operate in defined states to reflect their usability: empty (write pointer at start, no data written), implicitly open (automatically opened by a write command), explicitly open (opened via host command), closed (inactive but writable later), full (write pointer at end), read-only (writes prohibited but reads allowed), and offline (unavailable due to media errors).^[40] State transitions occur in response to writes, reads, or management commands, ensuring predictable sequential access patterns. Interface-specific constraints differ between ZBC and ZAC. Under ZBC for SCSI, the REPORT ZONES command supports partial reporting options to retrieve descriptors for subsets of zones, managing response times for devices with large numbers of zones. ZAC for ATA provides equivalent reporting capabilities without fixed limits on the total number of zones. Command latencies vary by operation and device. These standards have seen updates to accommodate evolving storage needs, with ZAC-2 (INCITS 549-2022) extending support for larger zone sizes—up to 1 TB or more—facilitating denser SMR and zoned SSD implementations while maintaining backward compatibility.^[50] ZBC-2 (INCITS 550-2023) similarly incorporates enhancements for expanded zone capacities.^[51]

NVMe Zoned Namespaces

The NVMe Zoned Namespace (ZNS) command set, defined in the NVMe 2.0 specification (2021), provides a zoned storage protocol over the NVMe interface, applicable to SMR HDDs and zoned SSDs. ZNS aligns with ZBC/ZAC models, supporting host-managed zoning with commands for zone management (e.g., Zone Open, Close, Reset, Finish) and the Zone Append command for efficient writes. It enables up to 65,536 zones per namespace and is increasingly used in enterprise environments for high-performance zoned storage.^[52]

Drive Identification and Reporting

Shingled magnetic recording (SMR) drives are identified and their capabilities reported to the host using standard SCSI and ATA protocol commands, enabling the host to detect zoned storage support and configure accordingly for compatibility. In SCSI interfaces, SMR drives supporting Zoned Block Commands (ZBC) are detected via the INQUIRY command, which retrieves vital product data (VPD) pages indicating zoned capabilities; for example, the Block Device Characteristics VPD page provides details on whether the device is zoned and the number of logical blocks per physical block. The REPORT ZONES command (opcode 0xA8) further reports zone statistics, including the total zone count, zone types (e.g., sequential write required or conventional), zone capacity, and the maximum logical block address (LBA) per zone; a representative SMR drive might report over 50,000 sequential zones, each with a 256 MB capacity, allowing the host to map data placement optimally.^[49]^[53]^[54] In ATA interfaces, SMR drives supporting the Zoned Device ATA Command Set (ZAC) are identified through the IDENTIFY DEVICE command (opcode 0xEC), which returns a 512-byte structure containing capability flags, including support for ZAC commands and zoned operation; the host can then issue the REPORT ZONES EXT command to retrieve similar zone details as in SCSI, such as zone descriptors listing start LBAs, lengths, and write pointer positions. This reporting ensures the host can distinguish SMR from conventional drives and adjust I/O patterns to avoid performance degradation.^[55]^[56] Following transparency concerns and post-2021 industry practices, SMR drives are explicitly flagged by manufacturers through model listings and protocol indicators; for instance, Seagate maintains an official catalog classifying drives as conventional magnetic recording (CMR) or SMR based on model numbers, aiding procurement and compatibility verification without relying solely on command responses. Utilities such as hdparm for ATA IDENTIFY DEVICE output and sg_inq/sg_rep_zones from the sg3_utils package for SCSI INQUIRY and REPORT ZONES enable users to verify SMR presence and zone configurations directly on Linux systems. In hybrid SMR drives, which combine conventional and shingled zones, reporting can dynamically reflect the current zone allocation via extended REPORT ZONES responses, supporting adaptive host management.^[57]^[58]^[59]

Applications and Software

Storage Use Cases

Shingled magnetic recording (SMR) technology excels in archival and cold storage applications, where data is typically written once and accessed infrequently, aligning with the sequential write patterns that minimize shingling overhead.^[60] These workloads, such as backups and long-term retention, benefit from SMR's higher areal density, which enables greater capacity per drive without proportional increases in power or space requirements.^[33] In hyperscale data centers, SMR drives are deployed for petabyte-scale cold storage tiers, supporting massive datasets in cloud environments by reducing total cost of ownership through fewer drives and lower infrastructure demands.^[61] As of 2025, the SMR market is projected to grow from USD 2.8 billion to USD 18.5 billion by 2035 at a CAGR of 20.7%.^[17] For surveillance and media storage, SMR drives are optimized for continuous, sequential video recording in 24/7 environments, where high-capacity needs outweigh random access demands. Toshiba's S300 series, incorporating SMR, provides dense storage for multi-camera feeds, enabling efficient retention of high-resolution footage in systems like video archives and AI analytics servers.^[62] These drives handle workloads up to 180 TB per year while supporting up to 64 camera streams, with sequential transfer rates reaching approximately 184 MB/s, making them suitable for sequential media ingestion without frequent overwrites.^[63] In big data analytics, SMR integrates well with distributed file systems like Hadoop's HDFS, where log files and sequential datasets dominate, allowing clusters to leverage higher capacities for cost-effective scaling. Research demonstrates that SMR-adapted Hadoop environments can process large-scale sequential workloads with minimal performance penalties, enabling exabyte deployments to achieve 20-30% lower cost per TB compared to conventional recording drives.^[9]^[12] Emerging use cases include AI training datasets, which often involve infrequent updates to vast, static corpora stored in data centers. SMR's capacity advantages make it ideal for these write-once scenarios.^[64]^[65]

Operating System and File System Support

Shingled magnetic recording (SMR) drives require specific adaptations in operating systems and file systems to handle their sequential-write nature and zoned architecture, particularly for host-managed and host-aware modes that expose zones to the host for better control. In Linux, support for zoned block devices, including SMR, was introduced in kernel version 4.10 through the blkzoned driver, which enables the kernel to recognize and manage zoned storage semantics like sequential writes and zone resets. File systems have built on this foundation: Btrfs added zoned mode support starting with kernel 5.12 in 2021, allowing it to allocate data in append-only zones while maintaining compatibility with conventional modes. Similarly, F2FS (Flash-Friendly File System) includes native zoned support for host-managed SMR, optimizing for flash-like sequential patterns on HDDs. ext4 can be used on zoned block devices via the dm-zoned device mapper target, which emulates a conventional block device while enforcing sequential writes. Support in other operating systems remains more limited as of 2025. Windows, including Windows 11, primarily handles SMR drives in device-managed mode through standard drivers, with no native host-managed zoned support in consumer editions, though Windows Server versions enable Zoned Device ATA Command (ZAC) passthrough for advanced zoning control. macOS similarly relies on device-managed SMR via generic drivers in macOS Ventura and later, without built-in host-aware features for zoned operations. At the application level, databases and storage software have adapted to zoned namespaces (ZNS), a related NVMe standard that emulates SMR-like zoning on SSDs but influences SMR optimizations. RocksDB, for instance, incorporates ZNS-aware logging and compaction to reduce write amplification on zoned media. Ceph, the distributed storage system, has optimized its OSD (Object Storage Daemon) for ZNS since 2023, enabling efficient zone management in clusters. In 2025, NVMe over Fabrics (NVMe-oF) received extensions for zoned command sets, allowing SMR emulation in networked environments to bridge legacy HDDs with modern zoned protocols.

Advanced Features

Dynamic Hybrid SMR

Dynamic Hybrid SMR refers to a reconfigurable feature in shingled magnetic recording (SMR) drives that enables individual zones to switch between conventional magnetic recording (CMR)-like operation and shingled modes during runtime, providing greater flexibility for workload adaptation.^[66] This capability was proposed in academic research in 2019 and by Western Digital around 2018 via proposals to the T10 committee, building on zoned storage standards to allow firmware-level reconfiguration without hardware changes.^[66]^[59] The mechanism relies on zoned block commands, specifically the REPORT ZONE and ZONE SET commands defined in the Zoned Block Commands (ZBC) standard, to query zone status and reformat selected zones between CMR and SMR formats.^[67] For instance, a drive might initially operate all zones in CMR mode for high random I/O performance, then reconfigure approximately 20% of zones to SMR to expand capacity for sequential workloads, with each zone typically sized at 256 MiB for granular control.^[66] This dynamic allocation supports mixed access patterns by dedicating CMR zones to bursty random writes while using SMR for archival data. By enabling runtime adjustments, Dynamic Hybrid SMR adapts to varying workloads, balancing capacity gains from shingling (up to 25% density increase) with CMR's superior random I/O throughput, thus mitigating the write amplification issues inherent in pure SMR configurations.^[66] In evaluations, this approach has demonstrated reduced I/O latency and improved overall efficiency for hybrid scenarios, such as data centers handling both active and cold storage.^[68] It remains an optional extension in current specifications, including those evolving through the Open Compute Project and T10 standards as of 2025, with limited commercial adoption.^[67] Reconfiguration introduces overhead, with zone conversions taking approximately 16 seconds for a 2 GiB block (equivalent to several zones), during which I/O operations may be suspended or delayed to migrate valid data.^[66]

Integration with Emerging Technologies

Shingled magnetic recording (SMR) synergizes with heat-assisted magnetic recording (HAMR) by leveraging localized heating to reduce track width and enable tighter shingling overlaps, thereby boosting areal density beyond conventional limits. In HAMR, the thermal assist allows media grains to be written more precisely, facilitating greater track overlap in SMR configurations without excessive inter-track interference. Seagate's Mozaic 3 platform integrates this approach, with 40TB HAMR-SMR drives sampled to data center customers in 2025 and volume production slated for 2026, achieving areal densities of approximately 2.6 Tb/in² through 10-platter helium-sealed designs. As of November 2025, these drives are in sampling phase.^[69]^[70]^[71] Microwave-assisted magnetic recording (MAMR) similarly enhances SMR by generating oscillating magnetic fields that strengthen write signals for overlapping tracks, improving recording efficiency in shingled bands. Western Digital employs energy-assisted perpendicular magnetic recording (ePMR) alongside SMR in its Ultrastar series, as seen in the 28TB DC HC680 drive ramped up in late 2023, which uses shingled ePMR with elements for up to a 20% capacity uplift over non-shingled counterparts. This integration supports sequential workloads in data centers, with overlap efficiencies contributing to higher effective densities in nearline storage.^[72]^[73] Projections position SMR as essential for scaling to 50TB+ drives by 2027, combining with helium-filled enclosures to enable more platters and lower power draw for energy-efficient exascale storage in hyperscale environments. Both Seagate and Western Digital roadmaps emphasize SMR's role in HAMR and ePMR hybrids to reach 44TB in 2027 and 50TB by 2028, addressing the exponential data growth in AI and cloud infrastructures.^[74]^[75]^[76] Challenges in these integrations include thermal management in shingled HAMR zones, where uneven heat application can induce track curvature and degrade signal integrity, leading to higher bit error rates. Advanced error correction codes, such as low-density parity-check algorithms tailored for 2D interference, are thus critical to maintain reliability and read performance in overlapping regions.^[77]^[78]

Criticisms and Limitations

Performance and Reliability Issues

One of the primary performance challenges in shingled magnetic recording (SMR) drives arises from the constraints of their zoned architecture, which favors sequential over random writes. Sequential write speeds can reach up to 270 MB/s under optimal conditions, comparable to conventional perpendicular magnetic recording (PMR) drives. However, random input/output operations degrade markedly to 10-50 MB/s or lower due to the necessity of read-modify-write cycles across entire zones, leading to substantial write amplification. In benchmarks, random 4K writes on a 25TB host-managed SMR drive can fail under standard test conditions, achieving only 2 IOPS.^[79]^[12]^[80] This inefficiency manifests in elevated latency, with benchmarks showing SMR random write latencies significantly higher than PMR equivalents—often 2-10 times greater, with PMR around 10-12 ms and SMR exceeding this under mixed workloads due to zone cleaning and resource contention when open zones accumulate—primarily from zone cleaning and resource contention when open zones accumulate.^[19]^[81] Reliability concerns in SMR stem largely from adjacent track erasure (ATE), where writes to overlapping tracks can degrade data integrity on neighboring tracks, resulting in higher bit error rates (BER) than in non-shingled systems. While the industry-standard BER target remains 10^{-15} for error correction viability, ATE introduces elevated erasure risks that demand robust coding and signal processing to maintain data fidelity. Enterprise SMR drives typically carry MTBF ratings of 2-2.5 million hours, aligning with PMR standards, but zone-full conditions exacerbate wear through repeated read-modify-write operations, potentially shortening effective lifespan under heavy update workloads.^[82]^[83]^[84] Empirical testing underscores these issues; for instance, 2023 benchmarks by StorageReview on a 25TB host-managed SMR drive showed random write performance failing under mixed loads.^[79]^[19] Drive firmware plays a critical role in mitigation, with optimizations like background zone reorganization and media caching reducing write amplification by buffering non-sequential updates and scheduling cleans during idle periods. Nonetheless, unoptimized deployments—such as those involving frequent random overwrites without adequate idle time—can double power consumption during intensive rewrite phases relative to baseline operations, due to heightened head activity and platter seeks.^[85]^[86]^[33]

Industry Transparency and Adoption Challenges

The lack of transparency regarding the use of shingled magnetic recording (SMR) technology in hard disk drives (HDDs) came to a head between 2019 and 2021, when Western Digital faced significant backlash for incorporating undisclosed SMR drives into its WD Red NAS product line. These drives, marketed for network-attached storage applications, led to performance degradation and failures in RAID configurations due to SMR's sequential write limitations, which conflicted with the random write patterns typical in such setups.^[18]^[27] This controversy culminated in a $2.7 million class action settlement in 2021, requiring Western Digital to disclose SMR usage on affected products for at least four years and provide refunds to eligible purchasers.^[27]^[87] In October 2025, Western Digital launched an investigation into elevated failure rates in its 2020-era 2-6 TB SMR-based WD Blue and Red drives, attributed to fundamental flaws in the technology, reigniting concerns from the 2021 lawsuit.^[88] Adoption of SMR technology has been hindered by incomplete support across operating systems and file systems, particularly in enterprise environments where random write-heavy workloads predominate. For instance, systems like ZFS in TrueNAS have shown limited compatibility, prompting warnings against SMR use in high-availability setups and slowing the shift from conventional magnetic recording (CMR) drives.^[47]^[89] As of 2023, SMR HDDs represented a modest portion of the overall market, with shipments reflecting growing but not dominant acceptance amid ongoing concerns over interoperability. The SMR market is projected to grow from USD 2.8 billion in 2025 to USD 18.5 billion by 2035 at a 20.7% CAGR, driven by capacity demands, though enterprise hesitation persists due to integration barriers.^[90]^[17] Critics have highlighted misleading marketing practices, such as claims of full compatibility with CMR-based systems without clear SMR disclosure, which eroded consumer trust during the Western Digital incident.^[91]^[92] Industry observers have called for mandatory reporting of Zoned Block Commands (ZBC/ZAC) support in drive specifications to enable better informed purchasing decisions, especially as SMR proliferates in mixed-use scenarios.^[93] Recent developments show incremental progress in standardization and targeted adoption. Toshiba released a 24 TB SMR model in its S300 surveillance HDD series in November 2025, suited for sequential video workloads in AI-driven systems, demonstrating viability in niche applications.^[94]^[28] However, resistance remains strong in database environments, where SMR's write amplification can disrupt transactional integrity and query performance, limiting broader enterprise uptake.^[12]

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