September 28, 2023


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Comparison of magnetic recording technology: SMR vs. CMR

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Comparison of magnetic recording technology: SMR vs. CMR

Comparison of magnetic recording technology: SMR vs. CMR.


What is CMR magnetic recording technology?

CMR (Conventional Magnetic Recording) is a magnetic recording technology used in hard disk drives (HDDs) to store and retrieve digital data.

It is the traditional method of recording data on magnetic media, as opposed to the newer SMR (Shingled Magnetic Recording) technology.


In CMR, the magnetic recording media consists of small magnetic grains that are arranged in a random pattern on the disk surface.

The write head of the HDD generates a magnetic field that aligns the magnetic grains in either a north or south polarity, representing the binary 0s and 1s of the digital data.

When reading data, the read head detects the magnetic field from the media and converts it into electrical signals that can be interpreted as the stored data.


CMR technology has been widely used in HDDs for several decades, providing a reliable and cost-effective solution for mass data storage.

However, as data storage requirements continue to grow, the limitations of CMR have become more apparent.

One key limitation is the physical size of the magnetic grains, which ultimately determines the density of data that can be stored on the disk. As data tracks become narrower and the magnetic grains smaller, the risk of data corruption and interference between adjacent tracks increases.


To overcome these limitations, newer technologies like SMR and HAMR (Heat-Assisted Magnetic Recording) have been developed.

These technologies offer higher data densities by using different recording methods, such as overlapping tracks in SMR or using heat-assisted writing in HAMR.

While CMR continues to be used in many HDDs, these newer technologies are being adopted to meet the growing demands for higher storage capacities.





What is SMR magnetic recording technology?

SMR (Shingled Magnetic Recording) is a magnetic recording technology used in hard disk drives (HDDs) to increase data storage density.
It is an advancement over the conventional CMR (Conventional Magnetic Recording) technology.

In SMR, the data tracks on the magnetic media are partially overlapped, similar to shingles on a roof, hence the name “shingled.” This overlapping arrangement allows for narrower tracks and increased areal density, enabling more data to be stored on the same physical disk surface.


The write process in SMR is different from CMR. When new data is written to the disk, the write head creates a wider magnetic track that partially overlaps with neighboring tracks.

This overlapping causes the adjacent tracks to be modified or rewritten, which is known as a “side-write” operation.

The modified data in the adjacent tracks is then rewritten back onto the disk. This process is necessary to accommodate the narrower tracks and ensure data integrity.


However, the overlapping nature of SMR poses challenges for random write operations.

Modifying existing data or writing new data in the middle of a shingled track requires rewriting the entire overlapping portion, including the adjacent tracks.

This process, known as a “read-modify-write” operation, can introduce performance penalties and increase latency compared to CMR technology.


To mitigate these challenges, HDD manufacturers have developed techniques like drive-managed SMR (DM-SMR) or host-managed SMR (HM-SMR).

DM-SMR drives handle the internal management of data placement, while HM-SMR drives rely on the host system to manage data placement, making it more suitable for specialized applications.


Overall, SMR technology allows for higher data storage densities in HDDs but may have trade-offs in terms of random write performance compared to CMR technology.

It is particularly useful for applications that require large-scale sequential writes and can benefit from the increased storage capacity.



Comparison of the advantages and disadvantages of SMR (Shingled Magnetic Recording) and CMR (Conventional Magnetic Recording) technologies:


Advantages of SMR:

Increased Data Density:

SMR allows for higher data storage densities compared to CMR. By overlapping tracks, SMR can fit more data on the same physical disk surface, enabling higher capacity HDDs.


SMR technology builds on existing CMR infrastructure, making it a cost-effective solution for increasing storage capacities without requiring significant changes to the manufacturing process.

Sequential Write Performance:

SMR excels in scenarios that involve large-scale sequential writes. It is particularly advantageous for write-intensive workloads where data is written sequentially and can be optimized for efficient sequential operations.


Disadvantages of SMR:

Random Write Performance:

SMR faces challenges with random write operations. Modifying existing data or performing random writes requires complex read-modify-write operations that can impact performance and increase latency compared to CMR technology. This makes SMR less suitable for workloads that heavily rely on random write access patterns.

Write Amplification:

SMR’s read-modify-write operations can lead to write amplification, where modifying data in a track results in rewriting multiple adjacent tracks. This increases the overall number of write operations required, which can impact the drive’s endurance and longevity.

Specialized Management:

SMR drives often require specialized management techniques, such as drive-managed SMR (DM-SMR) or host-managed SMR (HM-SMR), to optimize performance and ensure data integrity. These management techniques may require additional software or hardware considerations.


Advantages of CMR:

Compatibility and Widely Adopted

CMR is the traditional magnetic recording technology that has been widely adopted and proven over many years. It is compatible with existing systems and does not require specialized management techniques.

Random Write Performance:

CMR technology offers better random write performance compared to SMR. It allows for more flexible and efficient random write operations, making it suitable for workloads with significant random write access patterns.

Mature and Reliable:

CMR has been extensively developed and optimized, resulting in a mature and reliable technology for data storage.


Disadvantages of CMR:

Lower Data Density:

CMR technology has limitations in achieving higher data densities due to the physical size of magnetic grains and the need for wider tracks. As a result, CMR may not provide the same level of storage capacity as SMR for a given physical disk size.

Limitations for Future Growth:

With the increasing demand for higher storage capacities, CMR may face limitations in meeting the future requirements of data storage without significant advancements in the technology or the adoption of alternative recording methods like SMR or HAMR (Heat-Assisted Magnetic Recording).


It’s important to note that both SMR and CMR technologies have their own strengths and weaknesses, and their suitability depends on specific use cases and workload requirements.



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