Seagate's Shingled Magnetic Recording tech layers tracks to boost bit densities

Since about 2006, hard drives have used perpendicular recording technology to store data. That method has enabled platter densities up to 1TB and drives as large as 4TB. Perpendicular recording is starting to bump into physical limits, though. Seagate says the read and write components of current technology can't get any smaller. Neither can the associated drive tracks, which are down to 75 nanometers in width.

According to the firm, a new approach is needed if areal densities are to continue their upward trajectory. That new approach is called Shingled Magnetic Recording, or SMR.

Shingled recording preserves the perpendicular bit orientation of its predecessor. However, it fundamentally changes the way in which those bits are organized. Instead of arranging individual tracks with space in between, shingled recording lays tracks on top of each other in a staggered fashion—much like the shingles on a roof.

Traditional (left) versus shingled (right) track layouts. Source: Seagate

As the diagram illustrates, the read head is much narrower than the write head. This size difference allows the tracks to overlap without affecting the drive's ability to read the data. The overlap poses a problem when data is rewritten, though. Because the write head covers the read portion of the next track, that data has to be "picked up" before the rewrite can occur. The displaced data then needs to be written back to its original location, displacing the data in the following track. And so on.

To prevent rewrites from cascading down too many tracks, Seagate arranges the tracks into bands. The precise layout of these bands will be different depending on the drive's target application. Increasing the number of tracks per band will raise the storage density, but it will also slow rewrite performance.

Seagate says it's already shipping drives with SMR technology, though the first product isn't set to debut until next year. That drive promises a 25% increase in storage density: 1.25TB per platter and up to 5TB per drive.

SMR looks like a clever technology, and I'm eager to test the first drives based on it. That said, Seagate needs a better promo video. This short introduction has nothing on HGST's classic Get Perpendicular clip.

Seagate will also have to convince folks that SMR is worth the rewrite penalty. That might be an easier task than topping a disco-infused technology demonstration. SSDs have long since replaced mechanical drives as the go-to solution for high-performance PC storage, relegating HDDs to secondary and high-density storage. SMR's benefits may outweigh the penalty for those applications.

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