What prevents a hard drive from spinning faster?

[jonmcc33]

I was asked a question by an individual about what prevents a hard drive from spinning faster, say to 100,000RPM.

I thought about it and figured it was motor limitations, the controller card and even heat.

He told me that it was oil. This is his answer to me, in verbatim:

"When the hdds are not in motion, the read/write heads rest in the oil, this protects the heads and the disks. When the hdd is spinning, the read/write heads ride a cushion of air to keep them off the disks, but there are times when the heads may move down and the oil once again, allows the heads to stay off the disks. It creates a layer for the read/write heads to travel into as opposed to scratching the disk and well...ruining it. The reason why hdds can't spin faster, is the fact that the oil won't be able to cling to the platters at higher speeds."

Is this true? I have never once read anything about this. If it is true please verify with a reference and if it is not can you please state what exactly limits a hard drive from spinning faster? Thanks!

 

[TuxDave]

Disregarding the fact that we probably couldn't read jack on a hard drive spinning at 100,000RPM? I would guess (in order)

1) Inability to deal with the heat of such a fast spinning platter
2) Inability to protect the platter at such a speed. I would assume that a small bump would end up disintegrating the platter.

There's probably more...

 

[jonmcc33]

Well, I'm sure at 100,000 RPM heat would be the major issue. I know that even 15,000 RPM SCSI drives run super hot.

I just don't get the guys question. If he was asking about such a high speed then obviously heat would be the answer. If he's wondering what prevents a 7200 RPM hard drive from spinning faster I'd say that the controller card is the answer since that controls the motor.

I don't know where he got oil from since everywhere I have looked, even Googled it, and couldn't find anything about oil bonded to the platter or anything.

 

[Mr Nasty]

Wear and tear on the bearings would be enormous at that speed as well as the everything that has already been mentioned, also the power needed to spin a motor that fast would be huge

 

[itachi]

when an hd isn't in motion.. it rests on the platter. when it starts spinning, a cushion of air develops underneath the heads.. there is no medium between it (aside from the magnetic layer). when something goes wrong and the head comes into contact with the disk while spinning, scratching of the disk is the less likely case. the more likely case is that you'll destroy the coils rendering the hard drive useless. if, by chance, the coils didn't get damaged but the disk did.. you'd have a crap load of bad sectors.. but it'd still work.

and aside from the physical limitations of the mechanical parts, you have the limitations of the electronics. as tuxdave said, the data would be garbage. if there was a high enough demand, i'm sure manufacturers could push something out.. but at a huge cost in disk density. at a rotational speed of 100k rpm the flux running through the coil might start to produce a capacitance that would inhibit any accurate reading of data.. and to compensate, a lower voltage would have to be used.. which would require heads that are that much more sensitive to detecting change in flux. however, i have no idea at what point capacitance becomes a factor.. or if it ever is a significant factor.

 

[cirthix]

relaibility. face it, its your hard drive, you dont want it to screw up even once in a billion actions

 

[jagec]

Originally posted by: jonmcc33
"When the hdds are not in motion, the read/write heads rest in the oil, this protects the heads and the disks. When the hdd is spinning, the read/write heads ride a cushion of air to keep them off the disks, but there are times when the heads may move down and the oil once again, allows the heads to stay off the disks. It creates a layer for the read/write heads to travel into as opposed to scratching the disk and well...ruining it. The reason why hdds can't spin faster, is the fact that the oil won't be able to cling to the platters at higher speeds."

Is this true? I have never once read anything about this. If it is true please verify with a reference and if it is not can you please state what exactly limits a hard drive from spinning faster? Thanks!

From my experience in taking apart tons of hard drives, never ONCE have I seen any oil.

The limitations are mostly the inability of the drive to read data at such a speed. That, and heat...

 

[GoHAnSoN]

the oil theory; that's full of BS....

 

[Spencer278]

Originally posted by: GoHAnSoN
the oil theory; that's full of BS....

But it is good BS. It makes senses before you go looking into the hard drive

 

[Gibsons]

At the risk of comparing apples to oranges, look at the biological centrifuges. The centrifuges that get above 10K rpm are usually refrigerated and have rotors made of solid aluminum. The ones that get above 20K typically require that the rotor is spun in a pretty hard vacuum (less air friction), rotors are usually made of titanium to deal with the G forces (up to 600,000 x G). Biological samples are more heat-sensitive and the rotors are (usually) larger than any hard drive so you can't make a straight comparison, but I think you get the idea.

Finally, when the speeds start to get up there, they can get dangerous... the walls of modern ultracentifuges are armored to keep the rotor, whether broken or dislodged from the spindle, inside the centrifuge and not flying through the lab. A quote from Beckman's website

"41 mm (1.63-in) heat-treated steel alloy armor ring surrounded by a 12 mm (0.50-in) steel vacuum chamber to provide full protection for the operator"

What happens when things go wrong

http://www2.umdnj.edu/eohssweb...nts/explosion.htm#High

We're looking at rotors of solid metal weighing several pounds vs a disk weighing.. maybe an ounce or two (?), but you can see that the energies involved at such speed aren't trivial.

 

[DrPizza]

from the physics perspective of engineering one:

centripetal force = v^2/r

double the velocity and you quadruple the force.
Once you pass the strength of the disk, the disk is going to fragment. (and not in a way that defrag utilities is going to solve )

Or, think of it this way... take a string, tie it to a brick. Start spinning it faster and faster above your head. You're going to reach a point where the strength of the string is exceeded by the required force on the brick to keep it moving in a circle - the string breaks and the brick goes flying.


Or, to borrow from my nic and use an analogy - take a hunk of pizza dough. Flatten it into a small circle (like a pizza)... start spinning it around *slowly* - everything is fine. Spin it faster - it starts to stretch into a bigger circle - problem for disks. Spin it fast enough - hunks of dough go flying.

 

[FrankSchwab]

Originally posted by: Gibsons
What happens when things go wrong

http://www2.umdnj.edu/eohssweb...nts/explosion.htm#High

Cool link. I liked:

The half-inch thick (!!!) sliding steel door on top of the unit buckled allowing fragments, including the steel rotor top, to escape

I think there are several fundamental limits to high speed disks.

1. Current platter sizes and materials limit the rotational speed. Spin them too fast, the stresses cause the platters to first stop being flat (they 'wave'), followed by shattering. This could be dealt with with improved platter materials and construction; the ultracentrifuges linked to above can spin a rotor at 100,000 rpm.

2. Heat/noise. Spinning something that fast in atmospheric air pressure creates a huge amount of frictional heating, and significant noise.
It seems this is an engineering problem, not a fundamental physical limitation; removing heat isn't rocket science. Perhaps one ends up with a new industry building aftermarket heatsinks for hard drives? I can see this 2.5" drive chamber with a 5" tall spiky aluminum heatsink and 120mm fan....

Perhaps the air pressure can be reduced inside the drive to reduce both heat and air turbulence effects. This would cause problems during startup/shutdown, there not being enough air to float the heads until a significant rotation is acheived. This might be resolved by allowing the air pressure to track the rotation speed - at low speed, atmospheric air pressure is maintained, as the speed increases the air pressure could be reduced. Again, all engineering problems as opposed to physics problems.

3. Data rate. Apparently, current drives are limited in their ability to get data off the disk. Looking at commercially available disk products, as drive speed goes up, drive capacity goes down. Simply put, at higher speeds the bits on the disk fly past the heads faster than they can be read, so drives have to write the bits bigger in order to be able to read them back, reducing capacity. This appears to be a physics problem, and not an engineering one.

Sure, we can build a motor that'll spin the platters at 100,000 rpm; sure, we can build platters that'll survive the speed; sure, we can design a head that won't get destroyed by shutdown/startup and will be able to fly above the disk; but can we effectively read/write anything to the disk at those speeds? I think the age of 2 GB drives is past us; but spinning at high speeds might require that as being the maximum density.

/frank

 

[Codewiz]

Originally posted by: FrankSchwab

Originally posted by: Gibsons
What happens when things go wrong

http://www2.umdnj.edu/eohssweb...nts/explosion.htm#High

Cool link. I liked:

The half-inch thick (!!!) sliding steel door on top of the unit buckled allowing fragments, including the steel rotor top, to escape

I think there are several fundamental limits to high speed disks.

1. Current platter sizes and materials limit the rotational speed. Spin them too fast, the stresses cause the platters to first stop being flat (they 'wave'), followed by shattering. This could be dealt with with improved platter materials and construction; the ultracentrifuges linked to above can spin a rotor at 100,000 rpm.

2. Heat/noise. Spinning something that fast in atmospheric air pressure creates a huge amount of frictional heating, and significant noise.
It seems this is an engineering problem, not a fundamental physical limitation; removing heat isn't rocket science. Perhaps one ends up with a new industry building aftermarket heatsinks for hard drives? I can see this 2.5" drive chamber with a 5" tall spiky aluminum heatsink and 120mm fan....

Perhaps the air pressure can be reduced inside the drive to reduce both heat and air turbulence effects. This would cause problems during startup/shutdown, there not being enough air to float the heads until a significant rotation is acheived. This might be resolved by allowing the air pressure to track the rotation speed - at low speed, atmospheric air pressure is maintained, as the speed increases the air pressure could be reduced. Again, all engineering problems as opposed to physics problems.

3. Data rate. Apparently, current drives are limited in their ability to get data off the disk. Looking at commercially available disk products, as drive speed goes up, drive capacity goes down. Simply put, at higher speeds the bits on the disk fly past the heads faster than they can be read, so drives have to write the bits bigger in order to be able to read them back, reducing capacity. This appears to be a physics problem, and not an engineering one.

Sure, we can build a motor that'll spin the platters at 100,000 rpm; sure, we can build platters that'll survive the speed; sure, we can design a head that won't get destroyed by shutdown/startup and will be able to fly above the disk; but can we effectively read/write anything to the disk at those speeds? I think the age of 2 GB drives is past us; but spinning at high speeds might require that as being the maximum density.

/frank

The next question would be WHY would you want to? Why not invest the engineering into making cheaper better solid state disks that don't have the physical drawbacks.

 

[bwnv]

Stiction
Don't know about any drives built after '98, but before the use of MR heads and the phasing out of iron oxide coating on the platters pretty much all disks were lubed.Also

Look under "Cause: Drive Side"

 

[jagec]

Originally posted by: bwnv
Stiction
Don't know about any drives built after '98, but before the use of MR heads and the phasing out of iron oxide coating on the platters pretty much all disks were lubed.Also

Look under "Cause: Drive Side"

Older drives used lubricants that created a "damn" effect between the two surfaces, also difficult to separate.

LOL!

 

[BurnItDwn]

Also sound. 10K drives are loug
15K drives sound like jets
I00K would shatter ear drums ....

 

[klaviernista]

The reason hard drive platters cannot be, or more accurately, the reason they are not spun faster then they are currently is two-fold:

1) Microwaviness (that is literally what the property is called in the art, I didn't make it up) of a hard drive platter has a direct impact on how fast the platter can be spun. The faster the platter spins, the flatter the it has to be, otherwise it will wobble as rotational speed increases. If the platter wobbles, this causes at least two problems. 1st, the distance between the head and the media will continuously change. As I'm sure you all know, magnetic fields decrease in intensity as distance from their origin increases. Thus, wobbling of the platter causes a signal to noise problem (closer to the platter=higher signal to noise, farther away=lower signal to noise). 2nd, if the platter wobbles the probability for a head crash occurring is manfestly increased. The signal to noise problem is a seriosu problem, especially when your are trying to record at the 25-100 GB/square inch level. The 2nd problem is self explanatory?
-Ever wonder why faster hard drives typically have much lower storage capacity (i.e. the WD raptor is only available in 37 and 74 GB flavors?) Its because its much easier and much cheaper to make small diameter platters ultra-flat as opposed to a normal full size platter. Most high speed drives utilize smaller platters with a high speed motor in order to spin at high speed. Smaller platters=lower recording capacity.

2) Expense. first, it is really really expensive to make ultra flat discs that are suitable for high rotational speed hard drives (at least compared to lower speed drives). Second, its much more expensive to produce magnetoresistive heads that are suitable for reading and writing data on platters spinning at 15000 RPM as opposed to 7200 or even 10000RPM. The MR head must be carefully engineered to be ultra sensitive (have low coercivity), yet not be influenced by external magnetic fields (other then those emitted by the media to be read), and all the while have a free magnetic layer (the magnetic layer where the magnetic domain rotates in response to the magentic fields emitted by the grains of the recording media) that is capable of rotating and resting at more then twice the speed of a conventional drive. Its not that faster drives can't be built, they can and have been built. They are just really really really expensive to manufacture.

As for the oil/lubrication theory. I'll put this to rest. Almost all magentic recording media use some form of a hardcoat and solid state lubricant on their surface. The vast majority of all recording media use a combination of either an aluminum oxide or diamond like carbon hardcoat with a perfluoropolyether or perfluoropolyester ester lubricant layer. The lubricant layer does not appear or feel oily for a couple reasons. 1) The lubricant layer is typically a solid state lubricant that is not an oil; 2) The lubricant layer often times is very very thin (tens of nanometers thick), and so it feels more smooth and slippery as opposed to oily.

The lubricant layer is an absolute necessity in any hard disc application, Magnetic heads float on a cushion of air that nowadays is only a few microns to a few fractions of a micron away from the surface of the media. Given that perfectly flat substrates are not a reality and that noiseless spindle motors are also a pipedream, the head inevitiably contacts the media at some point (though this is not what you typically think of as a head crash). The presence of the lubricant layer allows the head to "skip" off the surface (for lack of a better description) with little damage to either the head or the media (as opposed to hitting the media and sticking, which is your typically head crash). Lubricants do play some role in higher speed hard drives, in that the lubricant has to be more effective the faster the media is spun, but they are not one of the main factors holding back rotational speed.

Hope that puts this to rest. Feel free to PM me or post more if you have questions about recording media or hard drives. I read about this stuff for a living.

 

[jonmcc33]

Thanks. This really answered my question.

 

[klaviernista]

US PAtent 6819531 to Shiroishi teaches a hard disk apparatus having a 50 MB/s transfer rate where the platter is spun at 25,000RPM. The recording density is fairly low (5GB/square inch) compared to slower drives (50-100gb/siquare). But it is fast!