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How to Choose a Hard Drive Suitable for NAS? CMR vs. SMR Hard Drives Explained

When choosing a NAS hard drive, in addition to parameters such as capacity, spindle speed, and interface, you should also pay attention to the magnetic recording technology used by the drive. Currently, the common magnetic recording methods for mechanical hard drives include CMR (Conventional Magnetic Recording) and SMR (Shingled Magnetic Recording). The two differ in how data is written, so they may perform differently in scenarios such as sustained writes, random writes, and RAID.

This article introduces the differences between CMR and SMR hard drives and helps you choose the right drive based on your NAS usage scenarios.

What Are CMR and SMR?​

CMR Hard Drives​

CMR (Conventional Magnetic Recording) is a common magnetic recording method for mechanical hard drives, also often referred to as PMR (Perpendicular Magnetic Recording).

  • The tracks of a CMR hard drive are arranged side by side without overlapping each other: when modifying data, the corresponding track can be written directly, so it generally maintains relatively stable performance in scenarios such as random writes and sustained writes.

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SMR Hard Drives​

SMR (Shingled Magnetic Recording) increases storage density by partially overlapping adjacent tracks, allowing more data to be stored in the same physical space.

  • Its track arrangement is similar to roof tiles. This design increases storage density, but when modifying some already-written data, the drive may need to reorganize and rewrite the relevant data.

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  • Therefore, in scenarios involving frequent data modification or sustained writes, an SMR drive may need to perform more data reorganization, which can lead to reduced write performance. If you mainly use single-disk storage, media storage, data archiving, or backup, an SMR drive can be a suitable choice. If you plan to build a RAID storage pool with multiple drives, or if your NAS involves heavy sustained writes, random writes, data synchronization, and RAID rebuild operations, it is recommended to prioritize CMR drives.

How to Confirm Whether a Hard Drive Is CMR or SMR?​

Different hard drive manufacturers may label the recording technology of their products differently; some product specifications clearly indicate CMR or SMR. Before purchasing a hard drive, it is recommended to check the recording technology of the specific drive model on the manufacturer's official website and choose according to your actual usage scenario.

For better compatibility and user experience, it is recommended to refer to the Compatibility List officially provided by TerraMaster, to check drive models and applicable TNAS devices before purchase.