Western Digital Host-Managed SMR HDDs

SMR is an acronym for “Shingled Magnetic Recording,” an important technology utilized to increase capacity and enable lower cost per TB in hard disk drives.

It is primarily used in HDDs that populate the world’s largest cloud data centers. As the amount of data created continues to grow at an ever-increasing pace, cloud service providers are seeking ways to drive down costs to enable new applications and provide the benefits of cloud storage to simplify our lives and increase the value of the services they provide. Connected devices provide the opportunity to capture and share more rich data in the form of photos, video, and audio.

Hard disk drives represent the most cost-effective technology to store data, but the challenge is to continually increase capacity and the amount of data that can be stored on each disk, or “platter” in the drive. Increasing drive capacity and storage density provides multi-dimensional benefits. The cost per TB in the device is reduced along with the cost of the corresponding infrastructure in the data center, including real estate, racks, servers and networking equipment.

So how does SMR contribute to this cost reduction? Every platter in a disk drive stores data in a track format. To increase capacity, those tracks have to be written narrower and narrower, while maintaining some space or buffer between discreet tracks. This buffer has to be managed in the device to maintain data integrity, even though the physical environment may be challenging due to vibration created by the cooling fans in the system. SMR circumvents this challenge by writing the tracks in an “overlapping” fashion, much like the shingles on a roof; hence, the name “shingled magnetic recording.”

SMR significantly increases the capacity that can be stored on every disk, improving what we call “areal density” and lowering costs as described above. In a given generation of HDD technology, this could result in approximately 15% additional capacity with cost reduction at both the device and system level.

HDDs have historically used CMR, or “conventional magnetic recording,” without shingled tracks nor the requirement to manage sequential zones. CMR drives support completely random read and write operation. Increasingly though, cloud service providers are investing in host software and file systems that can manage the complexities of SMR to deliver cost savings to their customers at scale. This is a trend that is fundamentally re-shaping the cloud data center and will continue to deliver lower cost and higher value data far into the future.