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Seagate's lightbulb moment: Make read-write heads operate independently

Multi Actuator arms will boost data access as capacities grow

Seagate is increasing IO performance in disk drives by separating read-write heads into two separate sets which can operate independently and in parallel.

The heads are positioned at one end of actuator arms which rotate around a post at their other end to move the heads across the platter surfaces. Thus, with an eight-platter drive, each read-write head is positioned above the same cylindrical track on each platter and reads or writes to and from the same disk blocks on each platter's surface.

Seagate's Multi Actuator technology divides these eight heads into two sets of four, and they can move independently of each other. An animated graphic here shows them in operation.

"Half the drive's recording heads will operate together as a unit, while the other half will operate independently as a separate unit," Seagate said. "This enables a hard drive to double its performance while maintaining the same capacity as that of a single actuator drive."

Aaron Ogus, Microsoft Azure storage architect, was quoted by Seagate: "In most data center applications the additional capacity gains cannot be effectively utilized without improvements in device IO capacity. The dual actuator technology helps unlock additional IOPS [input/output operations per second] and allows cloud providers to make effective use of the new capacity gains."

"Cloud" here surely means on-premises users as well as public cloud providers.

Currently, operating systems read and write data to a single disk drive. With this dual actuator arm set, the drive is divided into two logical drives. We imagine this will need to be exposed to operating systems and to applications such as storage array controllers, databases and other disk block-addressing pieces of code.

seagate gif

"The host computer can treat a single Dual Actuator drive as if it were two separate drives," Seagate added. "This means the host computer can ask a single high-capacity drive to retrieve two different data requests simultaneously – delivering data up to twice as fast compared with a single-actuator drive."

The first iteration of this technology is having dual actuators. More may be forthcoming. It solves a problem with disk drive IO density falling as drive capacity rises. Disk IO latency will remain the same but a physical disk drive's sequential IO performance will rise.

Seagate said the technology is in "development to be deployed on products in the near future". It talks about its forthcoming Exos disk drives, which will use Heat-Assisted Magnetic Recording (HAMR) to boost capacity. This will be in pilot production in 2018 with full volume manufacturing coming late 2019.

Boosting disk drive IO rate is an idea that's long overdue. We can expect both WDC and Toshiba to develop their own multi-actuator technology, and possibly go beyond having two sets of arms to three or four. ®

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