Monitor SMR and CMR of hard disk: Why choose CMR for monitoring projects

Two recording methods

• CMR (Conventional Magnetic Recording): The tracks are independent of each other, only the target track is affected when writing, and the random writing performance is good.
• SMR (shingled magnetic recording): The tracks partially overlap like tiles, which increases storage density and reduces costs. However, when rewriting a certain track, it will affect adjacent tracks, requiring "read-rewrite-write-back" of the entire strip.

Why surveillance scenarios should avoid SMR

Monitoring is a typical multi-path continuous sequential write + periodic overwrite load. SMR hard drives will deteriorate significantly in the following scenarios:

• When multiple channels are written concurrently, the cache is quickly filled up, triggering a large number of stripe reorganizations, and the writing rate drops off a cliff.
• In the recording overwriting (loop writing) stage, the performance degradation is particularly obvious, and frame drops and recording interruptions may occur.
• When setting up RAID, the reconstruction process may be mistakenly judged as a bad disk due to response timeout, resulting in reconstruction failure.
• The temperature of some SMR disks increases under long-term high load, further shortening their lifespan.

How to identify

• Check the manufacturer's official specifications, and the model clearly marked CMR / SMR is the most reliable.
• Prefer enterprise-grade or surveillance-grade hard drives marked as "surveillance-specific/video surveillance". Such products usually explicitly use CMR.
• Be wary of products with significantly lower prices for the same capacity.
• You can check the manufacturer's model comparison table or consult the supplier for confirmation before purchasing.

Other points for monitoring hard drives

• 7×24 design: Supports continuous work. Ordinary desktop disks are designed according to 8×5, and have a high failure rate in long-term operation.
• Supports multi-stream writing optimization: The monitoring disk firmware has been optimized for writing video streams to reduce fragmentation.
• Seismic resistance and heat dissipation: Multi-bay chassis should pay attention to vibration and air ducts, and perform vibration reduction treatment if necessary.
• Lifetime Metrics: Pay attention to the MTBF and annual write volume (TB/year) metrics.
• Batch replacement: Disks in the same batch age at the same time, so it is recommended to stagger replacement times in the project.