It used to be thought that WD was betting big on a MAMR technology change — a big bang, as it were — like the change from longitudinal to perpendicular magnetic recording (PMR). Not so, says Dr Siva Sivaram, WD’s President of Technology and Strategy. Microwave-Assisted Magnetic Recording (MAMR) is part of WD’s energy-assisted perpendicular magnetic recording (ePMR) strategy. There will be a continuous stream of technology advances around ePMR, and MAMR is not being delayed.
We were briefed by Dr Sivaram after the OptiNAND news broke — the use of added embedded flash in a disk drive controller to provide NAND storage for drive metadata instead of storing it on disk. In its announcement, WD said: “we expect an ePMR HDD with OptiNAND to reach 50TB [in] the second half of this decade.” Which we took to mean full MAMR wasn’t needed until then.
What is full MAMR? It is surely the use of a write head with a microwave generator beaming microwaves at the bit area under the write head, making it more receptive to receiving a write signal setting its magnetic polarity. This enables smaller bits, greater areal density and higher disk capacity.
Two recent WD announcements do use energy-assist, but not in this way. The September 2020 18TB UltraStar DC HC550 and DC HC650 uses ePMR tech, applying an electrical current to the write head to lower the jitter and improve the strength of the write signal. This month’s OptiNAND adds a NAND-enhanced drive controller SoC to the mix, which processes drive metadata in a faster and more granular way, enabling tracks to be placed closer together and so raising capacity in a sample drive from 18TB to 20TB.
Dr Sivaram said: “MAMR is not being pushed away.” The ePMR technology applies to the drive’s data plane, whereas OptiNAND applies to its control plane. MAMR is part of WD’s overall ePMR technology — a series of improvements that electrically improve areal density. According to Dr Sivaram, “This is still on track.”
He says: “ePMR is a large bucket. All aspects of MAMR and HAMR are included within it.” The DC HC550/HC650 announcements referred to generation 1 of WD’s ePMR technology. There will be others. The 50TB ePMR disk prediction for the 2025–2030 period could well involve microwave use.
SMR and OptiNAND
Shingled Magnetic Recording (SMR) media disks could be one of the biggest beneficiaries of OpitiNAND technology. In an SMR write event modifying existing data on the drive, a whole block or zone of tracks has to be erased and rewritten with the new data inserted. The OptiNAND can make that operation faster, reducing an SMR drive’s write lag and bringing its performance closer to traditional drive performance.
The details were not revealed, but we might envisage that the size of an SMR write zone — the block of tracks treated as an entity — could be reduced, shortening the time needed for a data rewrite operation. We might envisage a 22 to 24TB SMR/OptiNAND drive could be coming.
Also, OptiNAND’s use means the drive’s control plane can run in parallel with data plane operations. When metadata has to be read from disk that is not the case.
Seagate and Toshiba
Dr Sivaram said: “We will have products across the board with OptiNAND.” WD is at an advantage, he says, because it has HDD and NAND firmware engineers sitting in the same room — because it makes both disk drives and SSDs. Its disk drive competitors, Seagate and Toshiba, do not.
Our thinking is that Seagate and Toshiba will be talking to NAND suppliers, such as Micron, Samsung and SK hynix, and perhaps cheekily Kioxia (WD’s NAND joint-venture partner), about adding their embedded flash to disk drive controllers.
Toshiba already uses the bias current technology to improve its disk write signals with its Flux Control MAMR concept.
In theory Seagate could use similar technology and so gain a capacity jump without going to HAMR — adding a laser heating element to its write head and reformulating the drive recording medium. Will it? That is a big, big question.
Seagate has a US disk drive head bias current optimisation patent — number 6115201 — for determining a maximum magnitude of bias current that can be safely applied to a head of a disc. It was filed in 1998. It’s a relatively small disk drive engineering world and we can imagine Seagate is well up to speed with the technology.
It would not be a surprise if, one, Seagate introduced its own bias current/flux control technology and, two, both it and Toshiba added NAND to their disk controllers to store drive metadata data off the disk, process it faster, and raise areal density.