Seagate has said it's shipped a million shingled disk drives to date.
Shingled Magnetic Recording (SMR) increases a device's capacity by squeezing more readable tracks of data onto a platter's surface, albeit by hammering rewrite speeds.
When committing bytes to disk, the tiny electromagnet in the disk head that writes the tracks is much wider than the adjacent coil in the head that reads data from the surface. In other words, tracks can be thin when read but are wide when written.
If you partially overlap tracks when writing, leaving just enough width per track for the read coil to pick up, you can fit more information onto the platter than drives that don't overlap tracks. These overlaying tracks are grouped together into bands with gaps either side.
Unfortunately, therefore, when the data in an existing thin track needs to be updated, the head's wide write electromagnet will obliterate the adjacent track partially covering it. So, this adjacent track and all subsequent overlapping tracks to the end of the band must be read, stored in chip memory, and written back after the update operation.
Shingling drives slows down write access speeds, although reads are unhindered, we're told. In the diagram below, in a given band N, the magnolia-coloured tracks must be rewritten after the orange-coloured area is updated. The tracks in green can remain untouched.
Seagate SMR band structure.
We touched upon Seagate's SMR boffinry here last month. The tech gives rise to 1.25TB platters, and 5TB-plus disk drives. The company expects shingling to increase a device's capacity by up to a quarter, and such disks should be used for read-intensive applications.
Seagate says SMR drives should provide better value because SMR gear uses the same number of platters as today's non-shingled drives but offers greater data capacities. Meanwhile, rival HGST is cramming more platters and heads into low-friction helium-gas-filled drives to ramp up storage capacity. Seagate suggests that increasing platter and head counts can decrease reliability.
As far as SMR drive value versus helium-filled drive value is concerned, that's a matter for supplier pricing tactics.
Seagate says we can find out more about the SMR technology on this webpage.
"The architecture of a band within an SMR drive is customised for the application in which the drive will be integrated," the disk giant states. "Each drive family addresses its specific product needs and uses SMR to deliver the best results by application."
In other words, there will be different SMR hard drive models touted for different use cases.
The company is not saying exactly when the hoi polloi can order capacity-boosted SMR drives, although it will be sometime in 2014, nor how much the hardware will cost or what branding it will use.
In a statement, Seagate declared "it has shipped over one million drives using shingled magnetic recording". That's shipped, not merely manufactured. So its computer-making partners and others have been testing a million of these little suckers in one way or another. Drives boosted by the tech should at least be in the wild by next year. ®
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