This is also the case at elevation and higher temperatures.

True.
Gyroscopic precession however is possibly not accounted for, the impact might be greater than manageable.

Yes, you have a good point. So kids, dont mount your drives on angles.

But what about securely mounting a drive that vibrates a lot (instead of suspending it)?

I don't think there is universal agreement about the effects of drive suspension, just like there is not complete agreement about the mounting drives at an angle. As I recall, someone said that "Any harddrive made in at least the last 5 years can be mounted [without any negative impact] at any angle." And others agreed with that statement. But more recently, some have disagreed.

Any drive orientation with a horizontal axis of rotation (aka vertical drive orientation) will experience the greatest tendency for gyroscopic precession compared to any other orientation (assuming gravity is the cause, not some other force).

Bearing load is uneven when the drive orientation is any other than horizontal, being most uneven in a vertical orientation. Displacement of the disc axis would require that the bearings have a significant amount of play. These bearings have close enough tolerances that tens of g's of shock are within operational safety guidelines.

Actuator arms are strong enough to remain within operating tolerances during these same shocks in the tens of g's. They are capable of traversing the radius of the platter fast enough to produce seek times measured in milliseconds. They are functional horizontally, upside-down, and vertically. There are no different forces coming into play when operating in a non-orthogonal angle.

Air pressure is unaffected by orientation.

Using screws or suspension is just not the topic of this thread. That is the point both Straker and I try to make. There are already a gazillion threads on SPCR on this topic. So turning the second page of this thread into another discussion about drive suspension is pretty useless. If you want to discuss that subject anew, then start a new thread (not preferred, if you do you see why) or dig up an old one. But discussing two subjects at once in this already quite messy thread is not going to do much good.

Edit:
If you have trouble finding them, then try searching for seagate, whitepaper AND suspension.

I am happy for each to take their own views about orientation and mounting, but keep trying to remind folk:
1) Did you ever see a laptop instruction that said you must run the laptop in any particular orientation? I haven't; I haven't even seen an instruction that says do not change orientation while the drive (laptop) is in use.
2) We know drives mounted with 4 screws are still moving because we can hear the consequent vibration: mounting with zero screws doesn't bother me.
So IMHO, while the theoretical physics of these debates is interesting, practical physics says these effects are not reasonably measurable on my drives in the average life of my drives.

My god. And this is your second post?
My hat goes off to you, sir.


To the people who still don't believe, and are attempting to use half-understood physics to back up their claims: Draw a free body diagram of an component of the HD at horizontal, at vertical and finally at some oblique angle inbetween.

You will notice that all the same forces are in effect, pointing in different directions, and that the HD running at an angle is simple affected by the same forces operating in a direction which is average of the horizontal and vertical orientations.

A HD is exactly as likely to fail from 2 years running on a 45' angle as it would be if I ran it for one year horizontally and one year vertically. And since we've already determined that both those orientations are safe, the average of them must also be safe.

MP3 Players. Laptops. The Mac LCD screen computer. CarPCs. All these machines run at angles, and they do not drop like flies.




Whether or not there is agreement, this is a binary problem. Mounting on angles is either good or bad. I am either right or wrong. However, both theoretical and practical evidence weighs heavily on my side.

You may be correct (I am not qualified to judge), but it is somewhat interesting that Hitachi warns against mounting at angles. Presumably, they have engineers that know something about this subject. I am not saying they are correct, but it is a bit hard to dismiss it off-hand, at least from a theorectical view, without some good explanation as to why they are wrong.

Well, the head has a fly height of less than half a microinch (a human hair has a thickness of over 2000 microinches). I wouldn't say that "Displacement of the disc axis would require that the bearings have a significant amount of play."

Drives can take "shocks in the tens of g's" because the disc surface has a protective layer in case the head touches it. Actually the head is protected by the slider which also keeps it airborne.

If you mean it would actually be able to target data as usual "during these same shocks in the tens of g's" then you're dreaming my friend

I'm thinking that if the head operates continously under strange conditions the slider might now and then get discreetly grinded by the disc over a long period of time. One day the slider has been grinded away enough for the head to be exposed and when that happens the head will be destroyed on impact, so much for happy data retrieval days

Edit:
I'm not sure which direction gyroscopic precession would affect the disc axis in a vertical mount, I'll have to get back on that.

From a few discussions and my limited knowledge, I was told that the common symptom of temperature and pressure differentials are more sectors marked as bad and remapped than would be under constant good operating conditions. Catastrophic drive failure is less likely unless the drive is gonna fail anyway. I dont know if mounting at uneven angles will cause the same effect as temp/pressure changes, but other people think so so I'll go with that.

The biggest question is, what the fsck is the big deal. Why do you want to mount your drives at 45 degree angles? My drives were mounted at angles because the foam under them moved and compressed unevenly but it was only a few degrees off vertical. In any case it didnt cause problems.

WRT, laptop HDs they are built differently, have smaller platters, different electronics etc that they arent a fair comparison.

I think one reason it is a big deal (or maybe at least a small deal) is that if Hitachi is correct about drive angle, then maybe they are also correct about mounting a drive securely with all 4 screws to keep it from moving while vibrating.

Granted, a disk drive is not going to fail immediately if not mounted according to Hitachi instructions, and any differences would likely only show up as small statistical differences in reliability over a large sample of drives, but it does make one wonder if there is a sound theoretical basis for what they say.

Hitachi is just trying to save their ass, legally. It's like wearing a seatbelt. It only saves your life if you get in an accident, the rest of the time it's just there. But you still gotta use it all the time.


Anyway.

In custom designed cases, and in some suspensions, it becomes most space-effective to mount drives at an angle. This question comes up a LOT in the silent storage forum here, I was hoping we could provide a definitive answer that we could link people to instead of having to restate the same thing over and over.

I am aware of the fly height of the head. This does not change depending on the orientation of the drive. It is determined by forces larger than that exerted by gravity, otherwise merely turning the drive upside-down would render it unoperational.

I stated that "Displacement of the disc axis would require that the bearings have a significant amount of play." I did not state that the axis does not move. I believe everything I posted was merely an easily verifiable fact. I did not write with any particular conclusions in mind, so as to be objective. And by significant I do not mean large, or even perceptible on a human scale, I mean large enough to be a factor. For example, there is a myth that the coriolis effect determines the rotation of flow in a drain, or toilet, or what have you. In reality, this effect is so tiny that the rotation is much more sensitive to other factors.

I assume the "protective layer" does not lose its protective properties when the drive is mounted at an angle, and that the slider's durability remains the same regardless of drive orientation.

Let's say the head and arm assembly has a mass of 10 grams and the arm length is 10cm. The torque produced by gravity has an upper bound of 0.0098Nm if we also assume all the mass is concentrated at the very end of the arm. Let's say the axle length is 2cm, and the weight of the rotating assembly is 1kg, concentrated at the center of the axle (a reasonable estimate for center of mass). Then torque on the axle is 0.098Nm at most. The arm torque is inversely proportional to the drive's angle from horizontal, the axle torque (which would be the source of any gyroscopic precession) is directly proportional. Thus, as one rises, the other falls. Note, however, that the axle torque is an order of magnitude larger than the arm torque, so the sum is dominated by the axle torque over the majority of the range of possible mounting angles. Thus any combination is no more significant than the maximum torque on the axle alone.

Now let's say the rotating assembly does indeed exhibit gyroscopic precession. The frequency of precession for a 7200rpm drive will be about 1 full rotation in 5 seconds. This is based on my grossly exaggerated torque figure, the real frequency is likely to be less than half that. I would show you the math but it's long and I hope you don't think I have any reason to lie to you (though if you really insist I can post it). Let's say the radius of precession is 1mm (meaning, the bearing allows the end of the axle to be 1mm off axis). Pick a spot at the very edge of the platter. Deflection at this spot is around 1cm (peak to peak), once every 5 seconds. Already, I can see that 1cm is a ridiculous overestimate, but let's go on. Pick a spot on the very edge of the platter. Average magnitude of its y-velocity is then 0.002m/s. Its average y-velocity is zero, obviously, otherwise you will not find your drive where you last left it. The position of this point over time can be described sinusoidally, so with our average velocity figures, we can roughly estimate the maximum velocity achieved and we know the period over which this velocity increase occurs. Let's overestimate again and say y-velocity goes from zero to 0.01m/s in 1.25s (which is 1/4 of our period of rotation, the domain over which the wave goes from zero to peak). This is 0.008m/s^2 of acceleration. The head already counteracts acceleration of 9.8m/s^2, and can deal with 9.8m/s^2 in the opposite direction as well. This is a few orders of magnitude larger.

Even in this horrendously overestimated worst case, the changes brought about by the combination of gravitational and gyroscopic forces do not appear to be significant. If you disagree, please show me where I have made a mistake or invalid assumption. I'm sure there are bigger geeks out there than me (I hope...) or at least people much, much better with math and physics.


Likewise, thank you

D235hadow - I notice we were remiss on 23 April
Welcome to SPCreview - your posts are getting even better

This makes your calculation relative only if the head flies by itself above the disc rotating freely in space.

As everything is fastened the only disc y-axis acceleration to speak of will be while the disc accelerates. The head is allowed onto the disc containing data only after it's up to speed, so the operating head arm is never affected by acceleration in the disc y-axis by gyroscopic precession.
Anyway, at operational speed the disc axle is displaced as far as mechanically allowed and stays tilted in the same position.
As the head arm assembly is not internally affected by this force the head arm tension against the disc is altered. The result is impossible to calculate without the exact dimensions, mass, flexibility properties etc. of all the components in question.

I was going to suggest D235hadow for President, But ...

... I understood what he said, he understands what he said, he appears (no insult intended, I don't know enough to argue) to have knowledge on the subject he's talking about and he's willing to be corrected...

Sorry D235hadow, ...But I think you may have failed the in the main job criteria.


[on topic]: This is an interesting discussion, pray continue.


Pete

P.S. Sorry for assuming Genda

I contacted a few manufacturers with this question:


Answers as follows:



Maxtor was contacted by phone just to mix things up...
In retrospect I should have just emailed them like the rest.

Fujitsu only has live technical support.


Samsung's answer is pending. Hitachi I've already quoted above. Is that everybody?

Hyperslug : Thanks! That was a lot of good info.

There was an unresolved hypothesis that, while gravity alone and gyroscopic precession alone do not bring the disc out of spec, the combination of the forces brought about by them might. My calculations were intended to compare the effects of each. I am aware that the acceleration into the disc's final operating position will not be shared by the head, however I wanted to see if I could rule out that possibility if, in some hypothetical worst case, it did occur.

Now that we have established that the disc remains in one place during operation, I will examine whether or not the displacement caused by geometric precession lies outside the range of the head's adjustment. Let's assume that it is outside, and the head is incapable of adjusting to this displacement. If that is the case, the head will drag along the surface of the platter (at least on one side of the platter). This will cause the head (assuming a GMR design) to overheat due to friction, and fail to function.

However, empirical evidence strongly suggests that drives can indeed perform read and write operations at non-orthogonal angles. This in turn suggests that any displacement taking place in an angled drive must be within the limits of the head's ability to adjust its flying height. Since we have established that the disc's displacement does not change during operation, the head will then not need to adjust for any change in displacement during operation. Changes in the relative positions of the head and platter must be caused by a change in some force acting on them. However, as the forces acting on each are static, it does not appear that gyroscopic precession causes contact between them.

Additionally, keep in mind that the head suspension and air bearing is intended to be an adaptive system for attaining proper flying height. It must adjust for different conditions of air pressure, temperature, etc. This air bearing is a cushion of air pressurized between the slider and platter, that only forms in close proximity. It is not important exactly how much the arm tension on the head is altered by gyroscopic displacement of the platter, merely whether or not the force of the air bearing is enough to overcome it, which it appears to be. Based on this, I remain unconvinced that, if operating hard drives at non-orthogonal angles is unsafe, gyroscopic precession is the cause.

Gyroscopic precession might affect hard drive performance by altering the head's tracking. The head is guided into tracks by a closed loop servo system. Drives also perform calibration of this tracking (mainly to counteract thermal causes of misalignment) at set intervals. I can hear my seagate 7200.7 do this once in a while if i place my ear in front of my case. Since the servo system is designed with this adaptability in mind, I do not think this issue is of much concern. Seagate does, however, note that their performance optimizations have been done with orthogonal orientations in mind. It's likely only a well-controlled benchmarking experiment would answer this satisfactorily.

Hyperslug, thanks for bringing us information from the manufacturers' customer service. I don't know what to make of it, since some say angled mounting is ok, some say it is not. If anyone knows a hard drive engineer who could explain why we should or should not worry about this issue I think we would all love to hear from her/him. Maybe only drives from certain manufacturers can be tilted?

Peteamer, thanks, and no worries, you assumed correctly anyway.

And dukla2000, thanks for the warm welcome I enjoy reading this forum because there's much less pig-headedness and fanboyism here than at your average computing forum.

Thanks for keepin it real Hyperslug

Western Digital seems to have gotten this question before, it's straight forward and leaves little room for misinterpretation.

Seagate's answer doesn't seem like a first either. It starts hopefully mentioning that "The balanced rotary arm actuator design of the drive allows it to be mounted in virtually any orientation, including diagonally." However the homerun is cut short with the "*NOTE: These are the two preferred mounting orientations." Somehow I don't like the use of the word 'preferred' in this case.

Maxtor's phone call answer, is it a quote or written with your own words? Still don't like the use of that word mentioned above. Anyway, I'm with you on the retrospect conclusion

Fujitsu's reaction looks good. The answer is first confirmed, then answered with a maximum tolerance number, followed by a technical explanation revealing the weakness. Afterwards it's also backed up with reference material without question.
The tolerance number and the product's target market suggests that they have done thorough testing. I don't think they just throw out a percentage number like that for an enterprise product without any statistic reason. In reality that number surely variates a bit at different operating conditions and all drives are not created equally, but there is something behind it.

Back to Gyro:

Think of a spinning disc tilted by gyroscopic precession so the 'right side' of the disc is constantly higher and the 'left side' lower. The head hovers above the inner part of the disc on the 'right side' of the axle. The head is able to remain airborne when it's left alone. However when it's moved by the actuator to the right on the tilted disc it goes 'uphill'. The actuator can not know that the disc is tilted and when it rips the head full speed to the right it will be straight to the right perpendicular to it's own axle. The speed throws the head into the disc and drags it 'uphill' until it stops or slows down enough so the head lifts from the disc again. If it goes to the left it goes 'downhill' and the faster it accelerates the higher it flies above the disc. When it stops or changes direction the air cushion might not be able to take the fall.
So in this case gyroscopic precession causes head crashes even though it's a static force.

Something I wonder about:
With the arm y-axis at an angle can the actuator in operation amplify the force of gravity? Is there any way the actuator in some moment can partly throw the head in the same axis as gravity due to arm y-axis flexibility?

xilencer, time for you to help a perplexed dummy here...

If the Hard Drive is stationary, either bolted/screwed down or held relatively rigid by suspension, where does the input force needed for gyroscopic precession come from?
From the little I understand the force has to be a 'motion force' not a static force as would result on the bearings in a static though angled Hard Drive...

As I understand it your scenario above would only happen if the Hard Drive was in a constant rotating motion...

Can you fill in the bit I'm missing...


Pete

It seems a little ridiculous to me that some brands of HDs could be mounted obliquely and others couldn't.

I think what's more realistic is that some manufacturors are just trying to limit their liability.

Perhaps, but why would they be concerned about limiting their liability if there is not at least some basis for what they say?

There are not really enough drives mounted at other than 90 degree angles for them to worry about within the warranty period (usually one year). And they cannot really limit there liability, since there is no way for them to know how the drive was mounted if returned under warranty.

Why ridiculous? If it needs modifications to achieve (or even just testing to validate that it won't have negative effects). For instance, WD might think why should they waste money on validating this when we could spend the time on making the drive faster, whereas Seagate might think that this is a more important feature (maybe an OEM who wanted to mount a drive at 45 degrees) so they make sure that it can do that.

Samsung responded by email with "Call 1-800-SAMSUNG", so I did.

BTW, both phone conversation (Samsung & Maxtor) quotes are verbatim or really close. So here's the break down
So...

Manufacturers say: In general, stick to 90 degrees.

In practice: 90 degrees is definitely safe with recent drives. Odd angles are probably safe with recent drives, but no authoritative / controlled tests have been released to the public proving or disproving this.

In theory: ??? (D235hadow and xilencer will submit their thesis shortly.)

The bit you're missing is Gyroscopic Inertia possessed by the spinning hard disc in the drive.
Shouldn't be too hard to find more info on the web
_

My conclusion:

Since only horizontal and vertical disc axis mountings are free from gyroscopic precession,
I still believe this is why HDD manufacturers recommend mounting perpendicular to gravity.

How does Gyroscopic Inertia become gyroscopic precession in a hard drive whose chassis is stationary...

I can find nothing on the Internet that tells me how to provoke gyroscopic precession in a 'stable' gyroscope without actually moving the axis...



I'm humbly asking for your knowledge to be shared with me/us that are stumbling on this bit...

How does a gyroscope spinning on a fixed axis have gyroscopic precession introduced to it?

If you don't realise which bit I'm missing/not understanding or don't know the answer or don't wish to help a fellow forum member broaden their knowledge... feel free to suggest I " Look on the Web"...


Pete