Western Digital found itself in a dustup recently because it shipped shingled media recording (SMR) hard drives as RAID and NAS drives. What is shingled media recording? And why should you avoid it in RAID? And should you avoid it in general use too?
Shingled media recording 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 works
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 these 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 are fine for storing data that’s read frequently but rarely read, 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. And you’ll read the data back much more frequently than you copy files to it.
But for general use, such as using it to store your operating system and software you run, they 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 a conventional hard drive that doesn’t use SMR.