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SMR hard drives

Western Digital found itself in a dustup in the summer of 2020 because it shipped shingled media recording (SMR) hard drives as RAID and NAS drives. What is shingled media recording? What are SMR hard drives? And why should you avoid it in RAID? And should you avoid it in general use too?

Shingled media recording, or SMR, takes advantage of a quirk in the way drives write versus read that allows tracks to overlap, like shingles on a house. This increases storage and decreases cost, but decreases performance. Non-sequential writes, also known as random writes, suffer in performance greatly.

How shingled media recording (SMR) works

what is shingled media recording

Shingled Media Recording, or SMR hard drives overlap your data, which saves you money but hurts performance if you save and re-save files frequently.

Reading data takes less space than writing data, at least on a hard drive. This allows SMR drives to overlap tracks slightly, packing data in more tightly. This allows for very high-capacity, cheap drives. And when you read data, there’s no impact to performance.

The problem is there is impact to write performance. When you write to a track, you have to rewrite the overlapping track too. This cuts write speeds in half. More than half, since you have to account for seek time. It’s just like on a roof. When you replace a shingle, you have to replace the one overlapping it too. You never fix just one.

When you write to one area of the disk followed by another, performance drops even more due to the seek times coupled with the double-write penalty.

That makes SMR hard drives a liability in RAID and NAS applications because RAID and NAS will rewrite files from time to time to rebalance the data. It also makes them a poor choice as a general purpose drive, such as your computer’s C drive.

When to use shingled media recording (SMR) drives

SMR drives provide adequate performance for data you read frequently but rarely change, such as your music or movie collection. Write performance in that case isn’t a big deal, since you’ll just copy the data to the drive once and probably never erase a file. Copying the data to the drive will take longer than on a conventional drive, but you’ll do that once, then use the drive for years. And you’ll read the data back much more frequently than you copy files to it. The caveat is that at least one data recovery firm, Secure Data Recovery, believes SMR hard drives are less reliable than conventional drives. While they didn’t provide statistics, they observed that SMR causes more stress and wear on platters, heads, and actuator arms, leading to earlier failure.

And for general use, such as using storing your operating system and software you run, SMR drives perform very poorly. If you intend to use your drive for running programs, or writing data that might ever change, avoid SMR drives. Buy an SSD instead. Or buy a conventional hard drive that doesn’t use SMR, also known as a CMR hard drive. Use the SSD or the CMR drive to store your operating system, apps, and any data that you change frequently. Your system will perform much better.

Keep in mind that even though Western Digital‘s name is arguably more closely associated with SMR because it lost a class action lawsuit, Seagate and Toshiba also produce SMR drives. It was Seagate who produced the first SMR drives to hit the market in 2013.

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