This is more speculation around that topic.
1. What if we don't hit 7TB/platter, maybe only 4TB?
There have been any number of "unanticipated problems" encountered with scaling Silicon and Computing technologies, will more be encountered with HDD before 202?
We already have 1TB platters in 3.5 inch announced in Dec-2011, with at least one new technique announced to increase recording density (Sodium Chloride doping), so it's not unreasonable to expect another 2 doublings in capacity, just in taking what's in the Labs and figuring out how to put it into production.
Which means we can expect 2-4TB/platter (2.5 inch) to be delivered in 2020.
At $40 per single-platter disk?
That depends on a) the two major vendors and the oligopoly pricing and b) the yields and costs of the new fabrication plants.
Seems to me that Price/GB will drop, but maybe not to levels expected.
Especially if the rapid decline in SSD's/Flash Memory Price/Gb plateaus and removes price competition.
2. Do we need to offer The Full Enchilada to everyone?
Do laptop and ultrabook users really need 4TB of HDD when they are constantly on-line?
1-2TB will store a huge amount of video, many virtual machine images and a lifetimes' worth of audio.
There might be a market for smaller capacity disks, either through smaller platters, smaller form-factors or underusing a full-width platter.
Each option has merits.
The final determinant will be perceived consumer Value Proposition, the Price/Performance in the end-user equipment.
3. What will the 1.8 inch market be doing?
If these very small form-factor drives in mobile equipment get to 0.5-2TB, that will seem effectively infinite.
There is no point in adopting old/different platter coatings and head-manufacturing techniques for these smaller form-factors unless other engineering or usability factors come into play: such as sensitivity to electronic noise, contamination, heat, vibration, ...
4. The fifth-power of diameter and cube-of-RPM: impact of size and speed?
2.5 inch drives are set to completely displace 3.5 inch in new Enterprise Storage systems within a year. This is primarily driven by Watts/GB and GB/cubic-space.
The aerodynamic drag of disk platters, hence the power consumed by a drive, varies with the fifth-power of platter diameter and the cube of the rotational velocity (RPM).
If you halve the platter size (5.25 inch to 2.5 inch), drive power reduces 32-fold.
If you then double the RPM of the drive (3600 to 7200), power increases 8-fold,
a nett reduction in power demand of 4 times.
Changing platter diameter by square-root of 2 (halving the recordable area), the drive power reduction is 5.5-fold. This is the same proportion for 5.25::3.5 inch, 3.5::2.5 inch and 2.5::1.8 inch.
Reducing a 2.5 inch platter to 1.92 inches allows a drive to be spun up from 5400 RPM to 7200 RPM whilst using the same drive power, with 60% of the original surface area.
Whilst not in the class of Enterprise Storage "performance optimised" drives (10K and 15K), it would be a noticeable improvement for Desktop PC's, given they will also be using large SSD's/Flash Memory as well in 2020 and this will be solely for "Seek and Stream" tasks.
There is very little reason to "de-stroke" drives and limit them to less than full-platter access if they are not "performance-optimised". It's a waste of resource for exactly the same input cost.
5. Will 3.5 inch "capacity-optimised" disks survive?
Will everything be 2.5 or 1.8 inch form-factor?
There are 3 markets that are interested in "capacity-optimised" disks:
- Storage Appliances [SOHO, SME, Enterprise and Cloud]
- Desktop PC
- Consumer Electronics: PVR's etc.
Consumer PVR's are interested in Price/GB, not Watts/GB. They will be driven by HDD price.
The manufacturers don't pay for power consumed, customers don't evaluate/compare TCO's and there is no legislative requirement for low-power devices. Government regulation could be the wild-card driving this market.
There's a saying something like this I though made by Dennis Ritchie:
"Memory is Cheap, until you need to buy enough for 10,000 PC's".
[A comment on MS-Windows lack of parsimony with real memory.]
Corporations will look to trimming costs of their PC (laptop and Desktop) fleets, and the PC vendors will respond to this demand.
Already Enterprise and Cloud providers are moving to 2.5 inch form-factor to reduce power demand (Watts/GB) and floor-space footprint (GB/cubic-space).
Consumer and entry-level servers and storage appliances (NAS and iSCSI) are currently mostly 3.5 inch because that has always been the "capacity-optimised" sweet spot.
Besides power-use, the slam-dunk reasons for SOHO and SME users to move to 2.5 inch are:
- smaller footprint and higher drive count per Rack Unit.
- more aggregate bandwidth from higher actuator count
- mirrored drives or better, are possible in a small portable and low-power case.
- more robust, better able to cope with knocks and movement.
The 14-drive Copan 3.5 inch "Canister" of 4RU could be replaced by a 20-24 drive 2.5 inch Canister of 3RU, putting 3-4 times the number of drives in the same space.
6. What if there are some unforeseen "drop-deads", like low data-retention rates or hyper-sensitivity to heat, that limit useful capacities to the current 3-600GB/platter (2.5 inch)?
We can't know the future perfectly, so can't say just what surprises lie ahead.
If there is some technical reason why current drive densities are an engineering maximum, we cannot rely on technology advances to automatically reduce the Price/GB each year.
Even if technology is frozen, useful price reductions, albeit minor in comparison to "50% per year", will be achievable in the production process. It might take a decade for prices to drop 50% per GB.
I'm not sure how exactly designs might be made scale if drive sizes/densities are pegged to current levels.
What is apparent and universal, "Free Goods" with apparently Infinite Supply, will engender Infinite Demand.
If we do hit a "capacity wall", then the best Social Engineering response is to limit demand, which requires a "Cost" on capacity. This could be charging, as Google does with its Gmail service, or by other means, such as publicly ranking "capacity hogs".