# What happens with HDD if power is lost?



## Swamp Monster (Jan 22, 2011)

Do reading heads fall on platters when power is suddenly lost? What happens then? What if drive has NoTouch™ ramp load technology or similar, and what difference does it make?


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## scaminatrix (Jan 22, 2011)

My rig's failed/powered down/reset while in use hundreds of times, sometimes while crunching, sometimes while WinRAR's extracting etc. I would imagine this is the same thing, so I would guess, nothing would happen 999 times out of 1000.
Maybe you'd lose/corrupt data but not much worse.

Now watch me get bashed by a pro


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## freaksavior (Jan 22, 2011)

Usually nothing but it's certainly not good for it.

You want the drive to be able to stop reading/writing data before the motor shuts off but if you kill the power for example, it won't damage your drive, it will simply stop, I think that's the part of the reason you have a buffer.


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## Solaris17 (Jan 22, 2011)

I dont think they touch. Im almost certain HDD's are designed to stop at a certain point when the head drops. This prevents damage to the head and the platter. during power failure etc.


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## meran (Jan 22, 2011)

hmmm i havent heard any one here says that he lost his hdd from power lost but data corruptions happens allot from that sometimes windows doesn't boot but it doesnt die unless u knock ur case out


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## Swamp Monster (Jan 22, 2011)

For some time now I think that only bad thing that can happen when power is suddenly lost, is that HDD head can fall on spinning platter, and that shortens it's life. It is because WD says, that their new technology prevents head from touching the platter. I assume that if older models has not similar technology, then head *can* touch the platter. Data corruption doesn't bother me, only HDD health.

*edit* I found interesting material that confirms my suspicion:
http://www.google.lv/url?sa=t&sourc...682aCA&usg=AFQjCNHfGF-xEWDEHEa1NPcU4UYhvqSdyw

To me it sounds ankward that head is safely parked in area, that is bumpy/rough, but I guess it needs to be that way.


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## meran (Jan 22, 2011)

one time i bought a pc for someone i bought a hitachi 160gb and he drop it 3 feet from the ground i didn't work at all the hard drive have to power down it self in shut downs and windows just stop access it and power supply turn off nothing with heads or stuff


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## sneekypeet (Jan 22, 2011)

Only issue I have ever had from a improper shutdown was that when i rebooted, windows wanted to repair the drive or do a disc check. Either way, once they were done working their magic, all was good to go on the next boot. I wouldn't be too worried about it.


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## Swamp Monster (Jan 22, 2011)

The bad thing is - that heads really CAN touch platters, and damage them or head itself.
From that Pdf I understand that all these safety techniques work by informing controller, thus only if power is avaliable.


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## freaksavior (Jan 22, 2011)

Swamp Monster said:


> The bad thing is - that heads really CAN touch platters, and damage them or head itself.
> From that Pdf I understand that all these safety techniques work by informing controller, thus only if power is avaliable.



The heads float, it's not like a vinyl. 

Think of it like this,

the heads are giving the disk a blow job, they can't be rough with it or they will damage the goods. 
So power failure doesn't = bad blow job
power failure = finished blow job, that's all


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## Swamp Monster (Jan 22, 2011)

freaksavior said:


> The heads float, it's not like a vinyl.
> 
> Think of it like this,
> 
> ...



But when power suddenly disappears they don't float anymore - they land on goods and when drive spins up next time, goods get damaged


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## Frick (Jan 22, 2011)

Swamp Monster said:


> But when power suddenly disappears they don't float anymore - they land on goods and when drive spins up next time, goods get damaged



I don't think they ever touch the plates. If you ever tear a harddrive apart you'll notice the buggers is hard to budge.


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## Swamp Monster (Jan 22, 2011)

Frick said:


> I don't think they ever touch the plates. If you ever tear a harddrive apart you'll notice the buggers is hard to budge.



I have included Pdf file in my second post, did you read it? Maybe you have good, new HDD model, and something has changed?


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## Frick (Jan 22, 2011)

Swamp Monster said:


> I have included Pdf file in my second post, did you read it? Maybe you have good, new HDD model, and something has changed?



I read it now real quick, and the second paragraph says:

"All drive manufacturers have an auto park feature that safely parks the heads over the landing area when drive is spinning down".

It seems like they can land on the surface, but the manufacturers have taken steps to avoid it, that HP thing just one of them. Interesting.

EDIT: Maybe this is done magnetic somehow? There are some strong ass magnets in harddrives.


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## scaminatrix (Jan 22, 2011)

freaksavior said:


> the heads are giving the disk a blow job, they can't be rough with it or they will damage the goods.
> So power failure doesn't = bad blow job
> power failure = finished blow job, that's all



That's the best hard drive analogy I've ever heard!


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## Frick (Jan 22, 2011)

Swamp Monster said:


> The bad thing is - that heads really CAN touch platters, and damage them or head itself.
> From that Pdf I understand that all these safety techniques work by informing controller, thus only if power is avaliable.



It actually says how it works in the PDF, look at the picture provided.


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## meran (Jan 22, 2011)

freaksavior said:


> The heads float, it's not like a vinyl.
> 
> Think of it like this,
> 
> ...



LOL thats the point


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## theonedub (Jan 22, 2011)

Frick said:


> I read it now real quick, and the second paragraph says:
> 
> "All drive manufacturers have an auto park feature that safely parks the heads over the landing area when drive is spinning down".
> 
> ...



Deconstructed: Hard Disk Drive   
http://www.youtube.com/watch?v=-YHhzQJWOtE

Heads never touch.


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## Frick (Jan 22, 2011)

theonedub said:


> Deconstructed: Hard Disk Drive
> http://www.youtube.com/watch?v=-YHhzQJWOtE
> 
> Heads never touch.



So it's true then? Then why is it mentioned in that PDF document? Granted it is from 1999, but still.


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## Perseid (Jan 22, 2011)

Many years ago, hard drives heads used to stop wherever they were when the drive lost power. If you then moved the computer, the motion could cause the head to bump the drive. At best you scratch the platter and lose some data. At worst you snap the head right off. There used to be programs for DOS that would manually park your HDD before you turned the computer off in case you were going to put the computer in a vehicle or something.

Heads now snap back when they lose power and this can't happen anymore.


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## theonedub (Jan 22, 2011)

I imagine the landing zone is away from the platters that store the data. So who cares what it does there, its not going to effect the data on the drive.


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## Swamp Monster (Jan 22, 2011)

theonedub said:


> I imagine the landing zone is away from the platters that store the data. So who cares what it does there, its not going to effect the data on the drive.



My point is that if power is lost, then heads never make it to the landing zone. I would be happy to know something based on facts, that it has now changed. If parking is done really fast by magnets, then it's cool, but I need a proper confirmation to be really sure.


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## ivicagmc (Jan 22, 2011)

I heard that the greatest damage happens when you start in an early, cold morning. Could be that distance between head and the platter is so small that it actually, because of shrinking, touches the platter?


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## theonedub (Jan 22, 2011)

Swamp Monster said:


> My point is that if power is lost, then heads never make it to the landing zone. I would be happy to know something based on facts, that it has now changed. If parking is done really fast by magnets, then it's cool, but I need a proper confirmation to be really sure.



I really hate to cite Wikipedia, but: 


Modern HDDs prevent power interruptions or other malfunctions from landing its heads in the data zone by parking the heads either in a landing zone or by unloading (i.e., load/unload) the heads. Some early PC HDDs did not park the heads automatically and they would land on data. In some other early units the user manually parked the heads by running a program to park the HDD's heads.

A landing zone is an area of the platter usually near its inner diameter (ID), where no data are stored. This area is called the Contact Start/Stop (CSS) zone.* Disks are designed such that either a spring or, more recently, rotational inertia in the platters is used to park the heads in the case of unexpected power loss. In this case, the spindle motor temporarily acts as a generator, providing power to the actuator.*

Spring tension from the head mounting constantly pushes the heads towards the platter. While the disk is spinning, the heads are supported by an air bearing and experience no physical contact or wear.

Basically what Perseid had explained.


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## meran (Jan 22, 2011)

ivicagmc said:


> I heard that the greatest damage happens when you start in an early, cold morning. Could be that distance between head and the platter is so small that it actually, because of shrinking, touches the platter?



OMG and why there is engineers in this planet what they do the take all considerations they took power cuts now dropping what else power surge protection?


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## Swamp Monster (Jan 22, 2011)

theonedub said:


> Deconstructed: Hard Disk Drive
> http://www.youtube.com/watch?v=-YHhzQJWOtE
> 
> Heads never touch.



I watched this video, and it says that:
"heads floats on cushion of air, created of the spinning discs - an absolutely essential cushion that prevents heads from crushing the disk." - the same as in that document, but the document says that if discs stops spinning and head is still above data surface, it can touch. It is logical, because then no cushion exists.


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## theonedub (Jan 22, 2011)

This is like beating a dead horse, read my post above. 

The residual spinning of the platter after power loss is enough to maintain the air bearing long enough for the heads to park (there aren't any brakes so they spin and gradually slow down).


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## Frick (Jan 22, 2011)

And Swamp monster, the PDF says exactly the same thing.


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## ivicagmc (Jan 22, 2011)

Here is something interesting I found I wont to share... Didn't know that there is lubricant in HDD 
HDD operation is heavily influenced by temperature. Bearings, both in the spindle motor (either BB or FDB) and in the rotary actuator (BB) rely on lubricants. The lubricant's viscosity, like any lubricant, changes with temperature. Thicker when cold, thinner when hot. Colder temperatures are more problematic, since the increased viscosity significantly "stiffens" the bearing, resultant drag is high and motors may not be able to achieve their minimum operating speeds. But high temperatures can cause the lubricants to fail, with obvious consequences. 

In addition, mechanical dimensions of the entire HDD assembly will change as a function of temperature (the HDD components are primarily comprised of Aluminum and Stainless, which have different coefficients of thermal expansion. This usually isn't so much of a problem, since the mechanical tolerances allow for this, but it can result in reduced performance. And significant temperature excursions can cause glue bonds (bearing cartriges are usually glued together) to fail and/or result in brunelled bearing races.

The recording heads are also affected by temperature. The critical parameter is something called "Fly Height", the distance above the surface of the disk at which the "Slider" rides on it's "Air Bearing". Too high (usually colder) can cause write and read errors. Too low (usually, hotter) can result in contact between the Slider and platter, permanently damaging the HDD. 

The disk surface itself is coated in a fine layer of lubricant. It's designed to provide some protection if the recording head (Slider) contacts the disk surface. Temperature effects this lubricant like any other. In particular, at very high temperatures the lube can "spin off" the disk, reducing the effectiveness of the protecting layer. 

The magnetics and electronics all behave differently as a function of temperature. Usually, the HDD is designed to compensate for the effects. But operating the HDD outside it's temperature limits can exceed the range of compensation, typically leading to read and write errors.

As a general rule, higher temperatures are worse in terms of HDD longevity but the HDD should generally work OK up until the point when something breaks. At cold temperatures the HDD may not work at all, but it is unlikely that attempting to get it going will do it any harm, it just won't work.

Mechanical shock and vibration are the enemies of HDD reliability. 

The recording head consists of a "Slider", which flies over the surface of the spinning disk (think of an Air Hockey puck and you'll get the idea). The Slider contains the read and write elements that allow data recording (think of a Cassette Tape recorder and you'll get the idea). The Slider is attached through a "Suspension" to the rotary actuator. The HDD positions the Slider at different radii across the Disk by rotating (think of a Phonograph Tone Arm and you'll get the idea). The "Air Bearing" created by the flying Slider is fairly robust, but shocks in the Z direction can force the Slider to contact the disk surface, and that's bad.

Desktop and Server drives use Contact Start Stop, the heads actually land on the disk surface when the disk is stopped. Mobile drives use something called "Ramp Load", the heads are lifted off the disk when the disk is stopped. For this reason, it is not a good idea to use a Desktop HDD in a mobile application. Desktop HDDs are prone to a kind of damage called "Head Slap" when stopped, and so are less robust when it comes to tolerating the types of mechanical shocks likely to be seen in a mobile application.

Data is located on the disk surface in a series of concentric tracks. Each track is divided in to segments called "Sectors" (think of Pizza slices and you'll get the idea). To locate data on the disk, the HDD rotates the Actuator to the target track, and then it waits for the desired Sector to rotate under the Slider and past the read/write elements.

The HDD has to control the Actuator very accurately, track widths are measured in microinches. Linear motion (in the X, Y, or Z direction) has very little effect on the HDD's ability to "Track Follow", the Actuator is balanced, but rotary motion (rotation around the Spindle Motor's Z axis) is very difficult for the HDD to handle. The HDD will monitor it's track position and abort read and write operations (and subsequently retry) if it's straying too far, so usually the worst effect of linear or rotary shock is reduced performance. However, very large shocks can result in mis-reads or mis-writes (the Slider strays on to an adjacent track while reading or writing). 

Vibration can excite resonances in the HDD's mechanical structure. Resonance has the effect of magnifying the vibration and it can result in the same kinds of errors and lost performance that large shocks will cause.


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## Swamp Monster (Jan 22, 2011)

theonedub said:


> This is like beating a dead horse, read my post above.
> 
> The residual spinning of the platter after power loss is enough to maintain the air bearing long enough for the heads to park (there aren't any brakes so they spin and gradually slow down).



I really didn't read your post above, I guess I was writing at the time. I now understand how it moves heads away, and how it gets power to do sow, thank you for the information.


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## theonedub (Jan 22, 2011)

Oh I see, well glad the info helped. I just saw that episode of Decontsructed on TV the other night


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## Swamp Monster (Jan 23, 2011)

ivicagmc said:


> Here is something interesting I found I wont to share... Didn't know that there is lubricant in HDD
> HDD operation is heavily influenced by temperature.



I remember that some time ago (when IDE was popular) it was common knowledge that if HDD is moved from one house to another in winter, than we put it in a towel, so it don't get cold. If I remember right, sealing material would get hard and crack, allowing dust to get in.

Anyway it is not a good idea to turn it on when it is cold, due to condensate danger


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## Solaris17 (Jan 24, 2011)

Swamp Monster said:


> I have included Pdf file in my second post, did you read it? Maybe you have good, new HDD model, and something has changed?



changed but controller communication was not what i was talking about. tech like parking the control arm etc etc is good, but whoever wrote that that wont make a diffirence during power failure is right. What im talking about is physical NOT a argument passed to the controller. At a cerain point the heads will stop because of physical limitation. Almost like a support bar or a net under a trapeize wire. the head before hitting the platter will be stopped by the lack of ability to go further. or the arm being stopped by an indent in the plastic. I can draw pics if you want but I dont think they will. Manufacturers think of this stuff. They dont just assume electricity flows forever.


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## Swamp Monster (Jan 24, 2011)

Solaris17 said:


> changed but controller communication was not what i was talking about. tech like parking the control arm etc etc is good, but whoever wrote that that wont make a diffirence during power failure is right. What im talking about is physical NOT a argument passed to the controller. At a cerain point the heads will stop because of physical limitation. Almost like a support bar or a net under a trapeize wire. the head before hitting the platter will be stopped by the lack of ability to go further. or the arm being stopped by an indent in the plastic. I can draw pics if you want but I dont think they will. Manufacturers think of this stuff. They dont just assume electricity flows forever.



Thanks for expanded explanation! I didn't fully understand what you mean't in your first post, because you wrote that "it stops" and I wasn't sure if you mean platters or heads and what direction, because I tought that it isn't enough for head to stop if movement is in horizontal position. From this post I understood all, it's very good. So I guess longer posts is beter for understanding


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