Until now, WD has wanted to use microwaves to increase hard drive capacity, but the process is not yet ready for the market. WD is helping itself with ePMR.
MAMR and HAMR are two methods of increasing hard disk capacity. MAMR, WD’s previous favorite, works with microwaves that push the magnetic particles on the disk surface into the correct orientation while writing – thus reducing the magnetic field strength required for writing, making the write heads smaller and increasing data density.
In developing MAMR, WD says it has come across a process that is somewhat simpler but still allows capacity increases. ePMR calls it WD, Energy-assisted PMR. The company won’t announce details of this until the first ePMR hard drives are launched on the market: The Ultrastar models DC HC550 (18 TByte) and DC HC650 (20 TByte), which have already been introduced, work with ePMR instead of MAMR technology, contrary to what was assumed at the time. They are expected to be launched on the market in the first half of the year. WD achieves the higher capacity of the DC650 with Shingled Magnetic Recording (SMR).
In addition, WD has presented a new roadmap for further capacity increases using ePMR technology in the coming years: By 2023 the technology should be good for drives with up to 30 TByte, at least when using SMR. Drives with conventional recording should store a maximum of around 24 TByte of data.
From 2023, WD plans to use MAMR or HAMR – there is probably no decision at present as to which technology will be used. MAMR is cheaper, but HAMR allows a higher data density. WD’s largest competitor, Seagate, has been working on HAMR technology for many years and plans to launch the first HAMR series model this year. HAMR (Heat Assisted Magnetic Recording) uses laser diodes to heat up tiny parts of the magnetic disk to several hundred degrees, thus facilitating their magnetization. MAMR and HAMR are often referred to by manufacturers as Energy Assisted Magnetic Recording (EAMR).
Further hard disk tricks
In a presentation at Storage Field Day 2020, WD Manager Carl Che also introduced further innovations in in-house hard drive technology. According to these, WD wants to further increase capacity through SMR technology, for example. With SMR, Shingled Magnetic Recording, individual tracks are written slightly overlapping, so that changes are more time-consuming. SMR divides the hard disk into SMR zones of usually 256 MByte, which have to be completely rewritten if even one bit is changed. WD wants to save space in these zones, for example by using larger ECC blocks and thus store more user data on the disk. In total, SMR recording is expected to increase capacity by up to 25 percent.
As the tracks become narrower as the capacities continue to increase, the heads must be positioned more and more precisely – Che spoke of the accuracy of one nanometer. To achieve this, WD is using triple-stage actuators in the DC550 and DC650, which not only allow more precise positioning but are also designed to find the track faster. This, in turn, should increase the IOPS performance that the drives can deliver.
In addition, WD – like Seagate – is working on drives with split actuators. With traditional hard drives, all heads move across the disks simultaneously; if the head stack is split into two, for example, the two can operate independently. This doubles the data transfer rate and, most importantly, the IOPS performance. The disadvantage, however, is that these drives then also require two connections, and thus behave like two separate hard disks. (ll)