SMR or CMR? Choosing the Most Suitable Hard Drive

Vũ Khôi

Author at Wotech Electronics Blog

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SMR or CMR? How do you choose the most suitable hard drive for different purposes?

Shingled Magnetic Recording (SMR) or Conventional Magnetic Recording (CMR)? Many people ask themselves this question while searching for the right hard drive for a given purpose. Different data recording methods behave differently, and as a result, each is sometimes better and sometimes worse, depending on the intended use.

In this guide, we'll clarify which data recording methods exist today, how they work, and how well they suit different applications.

Common hard drive recording methods (CMR and SMR)

The basic recording mechanism of a hard drive consists of a magnetic head writing data onto the platter — where data is stored. There are two common recording methods, CMR and SMR, with clear differences between them. CMR means conventional magnetic recording, used in drives with pure PMR technology (perpendicular magnetic recording).

SMR, short for Shingled Magnetic Recording, is the second recording method.

CMR

PMR, short for Perpendicular Magnetic Recording, is the method in which magnetization (recording) occurs vertically and horizontally, perpendicular to each other, on the magnetic platters. PMR is the successor to LMR technology (Longitudinal Magnetic Recording) and achieves up to three times higher data density than its LMR predecessor; the read/write head is optimized for this purpose, and vertical positioning capability also contributes to the solution. This approach was developed to reach capacities above 750 GB on a conventional 3.5-inch hard drive. With PMR technology, we can write data directly to its final storage location on the hard drive without overwriting previous data.

SMR

SMR, short for Shingled Magnetic Recording, performs overlapping writes, because it rests on the premise that the write head is larger than the read head. Therefore, the write head writes data very close to previous tracks so the data can still be read. However, the data of the next track gets overwritten, meaning the next track can be overwritten after a successful write process. If things don't go as planned, this "rewriting of data" continues. That can significantly slow down the write process. However, the advantage of this technology is that it achieves higher storage density than PMR.

Besides the standard controller cache, SMR drives also have an on-disk cache in the outer tracks. That's where PMR technology shows its strength. After writing, data is transferred from the controller to the SMR area as quickly as possible. On the one hand, this process saves disk space, but it also involves a major difference from CMR technology: if the faster on-disk cache fills up before the controller can transfer data to the SMR area, the cache must first be released/emptied or overwritten before new data can be stored there. Consequently, with large files, the transfer speed may drop after a certain amount of data because the cache fills up and must first be cleared.

Which purposes do SMR and CMR technology suit?

SMR hard drives are a suitable choice if they are used for data storage, or when a data-storage PC requires a high-capacity hard drive. They offer greater storage capacity and better energy efficiency, which makes them a solution suited to long-term data storage goals. Basically, SMR drives are not a good fit if the hard drive has to perform write tasks frequently and continuously, because that can lead to cache overflow. In those cases, a hard drive using the CMR recording method is definitely required.

A CMR hard drive is the right choice when data is stored at high or extremely high transfer rates. That includes music streaming, image processing for network-attached storage (NAS) servers, or surveillance camera (CCTV) systems.

Conclusion: SMR for long-term data storage, CMR for cases where write operations repeat frequently

Today, some manufacturers have replaced CMR with SMR technology to save costs — but in return, random write performance is significantly slower than CMR, especially when configured to run RAID.

SMR can be seen as a fairly new tactic by HDD manufacturers to increase storage density compared with "traditional" HDDs using CMR technology. However, this technology has the drawback of markedly slower performance than CMR in certain tasks.

Both technologies (SMR and CMR) have their own advantages and areas of application. In summary, you can use SMR technology when you want large hard drives at a lower cost and usually with lower power consumption, serving purely as data storage devices.

For frequent write operations and large data transfers at high speed — that is, when high transfer rates matter — a CMR hard drive is the top choice.

Learn more about Seagate's SkyHawk hard drives at https://nbg.seagate.com/vn-o-cung-camera-skyhawk

Article source: https://www.reichelt.com/magazin/en/smr-cmr-which-hard-drive-is-best-for-which-purpose/

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