SSDs are increasingly popular these days, but there’s still plenty of demand for large spinning disks in the enterprise sector and still some home users who prefer sheer capacity to raw speed when building a storage array. Both Seagate and Western Digital sell a variety of drives to fill this market space — and both companies stand accused of pulling a bait and switch on customers by pushing SMR (shingled magnetic recording) products without informing users of that fact.
Standard hard drives are built using PMR, or perpendicular recording. In an SMR drive, each track is partly laid over the next, forming a structure that looks like the shingles of a roof. The advantage of this method is that it allows for significantly higher data densities in the same physical platter. The disadvantage is, well, everything else. The image below shows the difference between them:
The problem with SMR drives is that when you overlap the tracks like this, it means that there’s no way to write to just a single track without affecting the data on nearby tracks. Writing data to an SMR drive requires that the drive scan multiple tracks at once and then rewrite them. There’s a significant performance penalty for doing so, and that’s not the only issue with SMR drives. Users have complained that SMR drives are so slow, you can’t use them when rebuilding a ZFS array, and that you can’t create a RAID array if you add an SMR drive to it. There are very good reasons, in other words, why customers need to know if they’re buying an SMR drive.
Western Digital disagrees. The company is shipping SMR drives in its WD Red family without disclosing this fact. Customers have already been burned by the swap. If you’ve already used PMR-based WD Red drives in your RAID array, attempting to include SMR drives may not work at all. According to Western Digital, the 8-14TB drives they sell are all based on PMR, while the 2TB-6TB parts are all SMR drives. The performance difference between the two is significant, with the 2TB -6TB drives in the 150MB/s to 180MB/s range, while the 8TB-14TB drives run at 198MB/s to 215MB/s. While SMR drives are cheaper to manufacture than PMR drives, none of the savings is being passed on to customers as far as we can tell.
It’s Not Just a Western Digital Problem
WD isn’t the only company lying by omission as far as which HDD tech its hard drives use. A number of drives in Seagate’s Backup Plus family are also reportedly using SMR instead of PMR, and again, they aren’t disclosing this fact to customers.
The reason the companies are hiding this information is because you likely don’t want an SMR hard drive. There’s a reason why these products have typically been reserved for the enterprise market. They’re slower than regular HDDs and they don’t always play nice with PMR drives or other file systems. There’s nothing wrong with buying an SMR drive if you know what you’re getting, but the experience of using SMR is different from a PMR drive. Furthermore, both Seagate and Western Digital do disclose whether a drive uses SMR or PMR in other products on their websites, which makes it more likely that both companies are trying to sneak substandard hardware out the door (as far as the consumer market is concerned) without having to acknowledge it. Random write performance on SMR drives is particularly bad, so if you have workloads that depend on it you absolutely don’t want to run them on an SMR HDD.
Western Digital and Samsung both need to make it clear when their products use SMR and to communicate to customers that these products may not meet their performance or compatibility needs. The difference between PMR and SMR isn’t academic. The two drive technologies are not equivalent, either in terms of compatibility or performance.
Generally speaking, ExtremeTech does not recommend buying an SMR drive for any ordinary consumer use unless you are familiar with the performance penalties that come with using these drives and are willing to live with them. Hard drives are slow enough already. Companies that fail to accurately disclose important specifications that relate to the performance of their products do not deserve your business. In this case, the difference between SMR and PMR is not a trivial one, and they know it.
Top image credit: Getty Images
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