Several hard drive makers have been under fire for quietly replacing some HDD models with ones that use a technology called shingled magnetic recording (SMR) instead of conventional magnetic recording (CMR). SMR drives generally do not perform as well, particularly in RAID environments. This prompted a couple of lawsuits against Western Digital, which slipped some SMR drives into its lineup of Red HDDs marketed for network-attached storage (NAS) appliances. In response, WD has rebranded its Red line and is finally being more transparent about what recording technology its HDDs use.

There is quite a bit to unpack there, and the best place to start is with the recording technologies at the heart of all the ruckus. CMR was previously known as perpendicular recording (PMR), with magnetic tracks that sit next to each other. As explained by Synology, writing data to a CMR drives works by “aligning the poles of the magnetic elements, which represent bits of data, perpendicularly to the surface of the disk.”

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