Last week WDC announced their next generation technology for hard drives, MAMR or Microwave Assisted Magnetic Recording. This is in contrast to HAMR, Heat (laser) Assisted Magnetic Recording. Both techniques add energy so that data can be written as smaller bits on a track.
Disk density drivers
Current hard drive technology uses PMR or Perpendicular Magnetic Recording with or without SMR (Shingled Magnetic Recording) and TDMR (Two Dimensional Magnetic Recording), both of which we have discussed before in prior posts.
The problem with PMR-SMR-TDMR is that the max achievable disk density is starting to flat line and approaching the “WriteAbility limit” of the head-media combination.
That is even with TDMR, SMR and PMR heads, the highest density that can be achieved is ~1.1Tb/sq.in. The Writeability limit for the current PMR head-media technology is ~1.4Tb/sq.in. As a result most disk density increases over the past years has been accomplished by adding platters-heads to hard drives.
MAMR and HAMR both seem able to get disk drives to >4.0Tb/sq.in. densities by adding energy to the magnetic recording process, which allows the drive to record more data in the same (grain) area.
There are two factors which drive disk drive density (Tb/sq.in.): Bits per inch (BPI) and Tracks per inch (TPI). Both SMR and TDMR were techniques to add more TPI.
I believe MAMR and HAMR increase BPI beyond whats available today by writing data on smaller magnetic grain sizes (pitch in chart) and thus more bits in the same area. At 7nm grain sizes or below PMR becomes unstable, but HAMR and MAMR can record on grain sizes of 4.5nm which would equate to >4.5Tb/sq.in.
It turns out that HAMR as it uses heat to add energy, heats the media drives to much higher temperatures than what’s normal for a disk drive, something like 400C-700C. Normal operating temperatures for disk drives is ~50C. HAMR heat levels will play havoc with drive reliability. The view from WDC is that HAMR has 100X worse reliability than MAMR.
In order to generate that much heat, HAMR needs a laser to expose the area to be written. Of course the laser has to be in the head to be effective. Having to add a laser and optics will increase the cost of the head, increase the steps to manufacture the head, and require new suppliers/sourcing organizations to supply the componentry.
HAMR also requires a different media substrate. Unclear why, but HAMR seems to require a glass substrate, the magnetic media (many layers) is deposited ontop of the glass substrate. This requires a new media manufacturing line, probably new suppliers and getting glass to disk drive (flatness-bumpiness, rotational integrity, vibrational integrity) specifications will take time.
Probably more than a half dozen more issues with having laser light inside a hard disk drive but suffice it to say that HAMR was going to be a very difficult transition to perform right and continue to provide today’s drive reliability levels.
MAMR uses microwaves to add energy to the spot being recorded. The microwaves are generated by a Spin Torque Oscilator, (STO), which is a solid state device, compatible with CMOS fabrication techniques. This means that the MAMR head assembly (PMR & STO) can be fabricated on current head lines and within current head mechanisms.
MAMR doesn’t add heat to the recording area, it uses microwaves to add energy. As such, there’s no temperature change in MAMR recording which means the reliability of MAMR disk drives should be about the same as todays disk drives.
MAMR uses todays aluminum substrates. So, current media manufacturing lines and suppliers can be used and media specifications shouldn’t have to change much (?) to support MAMR.
MAMR has just about the same max recording density as HAMR, so there’s no other benefit to going to HAMR, if MAMR works as expected.
WDC’s technology timeline
WDC says they will have sample MAMR drives out next year and production drives out in 2019. They also predict an enterprise 40TB MAMR drive by 2025. They have high confidence in this schedule because MAMR’s compatabilitiy with current drive media and head manufacturing processes.
WDC discussed their IP position on HAMR and MAMR. They have 400+ issued HAMR patents with another 100+ pending and 75 issued MAMR patents with 46 more pending. Quantity doesn’t necessarily equate to quality, but their current IP position on both MAMR and HAMR looks solid.
WDC believes that by 2020, ~90% of enterprise data will be stored on hard drives. However, this is predicated on achieving a continuing, 10X cost differential between disk drives and (QLC 3D) flash.
What comes after MAMR is subject of much speculation. I’ve written on one alternative which uses liquid Nitrogen temperatures with molecular magnets, I called CAMR (cold assisted magnetic recording) but it’s way to early to tell.
And we have yet to hear from the other big disk drive leader, Seagate. It will be interesting to hear whether they follow WDC’s lead to MAMR, stick with HAMR, or go off in a different direction.
Photo Credit(s): WDC presentation
2 thoughts on “Disk rulz, at least for now”
I can think of two reasons HAMR could have a problem with Al platters:
1: AL’s high thermal conductivity which would increase the amount of energy that has to be added to the spot being recorded and then dissipated from the drive. This would also reduce the time the spot is hot enough to write to and increase the amount of heating of adjacent data.
2: AL and the magnetic coating may have very different coefficients of thermal expansion. This would result in cracking and flaking of the platted/sputtered magnetic media
Howard, thanks for the comment.
I was thinking it might have something to do with heat. But thought glass would do a better job of dissipating the heat than AL but maybe it’s that AL is too fast to work well.
The thermal coefficient issue has to play havoc on servo for a head that that heats up one small spot on media, writes data and then moves onto the next spot on the track. I know it’s probably on the order of microseconds if not nanoseconds but still expansion and contraction has got to move grains in real time.
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