What factors cause HDDs end up with bad sectors besides impact damage?

[Widjaja]

Just something I have not looked in depth into since I have never had a HDD randomly die on me yet knock on wood.

Sure a HDD can get impact damage sue to negligence.
But what other factors can cause such an issue?

One job I am working on made me think about this since the drive has bad sectors, no obvious factors like lots of dust or poor quality PSU.

 

[LAN_deRf_HA]

Mechanical failures due to manufacturing imperfections either at the assembly or individual component level. Bonked circuit boards from bad power supplies or a surge. Though usually that doesn't cause disk damage and can be fixed by replacing the board. Software errors can also corrupt tables and what not but those are normally fixed by reformatting.

 

[micropage7]

some err come from mechanical failure, aging drive that lead to decreasing performance, placement like shocking, heat, high electro magnetix exposure etc

 

[erocker]

Things move, things wear out. Bearings, control arm, etc.

 

[twilyth]

Since modern drive heads float just a few microns over the platter and since any contact would result in a head crash, a bad sector is not going to be the result of impact damage - at least not in terms of there being any damage to the platter. You'll get a catastrophic head crash or nothing at all.

Also, since all drives now use a voice coil actuator which snaps back to the 'park' position when not actively in use, head crashes are extremely rare. It's not like with the old stepper actuators where if you didn't park them you risked having the head bounce into the platter even with the machine off.

 

[lilhasselhoffer]

If you ever get a chance, check out the manufacturing facilities for HDDs. It's a heck of an experience, and can enlighten you as to why the things fail.

1) Aging bearings. Variable speeds on the inside of a disc can produce unreadable sectors nearest the spindle. The bearings have crazy huge lifespans, considering they are generally magneto-hydrodynamic (basically, they float on magnets soaked in ferrofluids), but do eventually run out at some point. Small variances in speed matter a lot more at the center of a disc than on the outside.
2) Manufacturing imperfections. This is a general boiler plate. Manufacturing isn't 100% correct, and even if it is there can be variance due to chemical make-up, atmospheric conditions, and input materials. Anything produced has some sort of "imperfection." The question is whether or not the level of imperfections is tolerable.
3) Magnetic head damages. If there is any damage in the drive that moves the magnetic head (anything from material imperfections to poorly designed firmware) you're likely to develop some sort of error.
4) Degaussing. Magnetic storage requires that microscopic segments of memory remain relatively constantly magnetized over extended periods. Anything that small can be influenced by a myriad of external forces, so the blame for these bad sectors is -crap happens-.
5) The aforementioned mechanical jarring. Contact with the magnetic head will always screw up a perfectly good sector, and "contact" could mean permanent magnetization because the head got closer to the disc (doesn't have to be physical contact like most people assume).

While not comprehensive, the first three reasons are your most likely candidates in a desktop (no movement generally means no jarring). The same is true for a laptop, with the possible addition of the fifth point.

If you're looking for blame, don't. Trying to resolve HDD damage to any one of these issues is down to either looking for damage to the computer from having it dropped, or beyond the home user given the complexity of opening the HDD and having the necessary equipment.

 

[de.das.dude]

its mainly imperfections in the manufacturing of the platter that cause bad sectors. depends on the Q.C of that manufacturing unit / even the country.

 

[Jetster]

If you stand up or lay down a case or laptop when the drive is spinning can cause damage do to the giro effect.

Also extreme temperature change

Electrical shock wrong voltage, lightening

Magnetic field, microwave, x-ray

Luckly its not hard to check if a drive is damaged or wearing out. HDtune is a great program. I just used it to check a drive in a laptop that was working but it felt slow. So I check it. It passed all the tests but it was only reading 30 Mbs and would drop to 5 Mbs in big spikes. The replacement was reading at 60Mbs stable

IMO when a drive is starting to get bad sectors, its done. Buy a new one

 

[RejZoR]

I'd say there are just 2 main reasns for bad sectors. Physical damage like shock while head is above the platters and defects in materials and manufacturing process.

 

[Widjaja]

If you stand up or lay down a case or laptop when the drive is spinning can cause damage do to the giro effect.

Also extreme temperature change

Electrical shock wrong voltage, lightening

Magnetic field, microwave, x-ray

Luckly its not hard to check if a drive is damaged or wearing out. HDtune is a great program. I just used it to check a drive in a laptop that was working but it felt slow. So I check it. It passed all the tests but it was only reading 30 Mbs and would drop to 5 Mbs in big spikes. The replacement was reading at 60Mbs stable

IMO when a drive is starting to get bad sectors, its done. Buy a new one

HDTune is what confirmed the errors.
After this I went ahead with WD Diag software which also stated bad drive as it could not complete the quick test.

At the moment I am hoping the drive has completed a image copy on to the new one.
The drive was a WD Black 640gb and copying it over using Norton Ghost to a Seagate 1TB SV3.5.
After this I'll be checking the data on the new drive then doing a Vista Install Repair since the msshsq.dll was corrupted and the bad sectors were making the loading time take ages.

RejZOR's two points are exactly the same and only potential reasons I could think of as well.

But in this case it could be other things mentioned above by the previous posters as well.

 

[twilyth]

I want to point out once again that drive heads NEVER, EVER touch the platter.

http://www.howstuffworks.com/question60.htm

When a head touches the spinning platter that is called a head crash and you WILL, without any doubt in your mind, know what just happened.

This is a tech forum so it's important to get certain things right and this is one of them.

 

[Jetster]

You just contradicted yourself. They can and do touch the platter if you throw it hard enough

 

[Widjaja]

I think power surges may also be a possibility come to think of it.
Jetster would have touched on it by saying wrong voltage I guess.
A customer with an HP laptop found his machine stopped working after a power surge.
Thing is the machine itself is fine but the drive has bad sectors.
Fortunately Windows 7 was able to get the OS running but still ghosting over yet again with Seagate Acronis cloning utility which clones all partition of the drive on to the new one as long as they are seagate.

As for heads touching a spinning platter, but appear to be named under something different, I am sure they can still give bad sectors as I have had a external dropped and it ended up with one bad sector at the start according to HDTune.

 

[twilyth]

As for heads touching a spinning platter, but appear to be named under something different, I am sure they can still give bad sectors as I have had a external dropped and it ended up with one bad sector at the start according to HDTune.

Unless the drive was doing I/O at the time you dropped it, the head hitting the platter didn't cause the problem. Voice coil actuators are no where near the platters unless they are spun up and doing I/O.

 

[Widjaja]

Yeah it was read writing at the time I think.
It was quite a while back.
It was during the time the OS was reading the drive for data as I had just plugged in the external.
A few seconds later I dropped it from about 1ft.
Seagate ended up repairing the HDD again.

 

[de.das.dude]

I want to point out once again that drive heads NEVER, EVER touch the platter.

http://www.howstuffworks.com/question60.htm

When a head touches the spinning platter that is called a head crash and you WILL, without any doubt in your mind, know what just happened.

This is a tech forum so it's important to get certain things right and this is one of them.

schishhhhhhhhhhhhh chack chak chak chakchakchakchakchak....

 

[twilyth]

Yeah it was read writing at the time I think.
It was quite a while back.
It was during the time the OS was reading the drive for data as I had just plugged in the external.
A few seconds later I dropped it from about 1ft.
Seagate ended up repairing the HDD again.

Sorry to be like a dog with a bone on this point, but since the platters are spinning about 150mph from the head's point of view, any contact is going to be much more serious than a couple of bad sectors. I suppose it's theoretically possible that the head barely touched for just the tiniest instant, and ever so lightly so that only a few atoms from the head rubbed off on the platters, but that's not how it usually goes.

 

[Widjaja]

schishhhhhhhhhhhhh chack chak chak chakchakchakchakchak....

I am familiar with the noise.

Sorry to be like a dog with a bone on this point, but since the platters are spinning about 150mph from the head's point of view, any contact is going to be much more serious than a couple of bad sectors. I suppose it's theoretically possible that the head barely touched for just the tiniest instant, and ever so lightly so that only a few atoms from the head rubbed off on the platters, but that's not how it usually goes.

Fair enough

 

[Stevicus]

Every so often a piece of surface material loosens & dislodged by the armature to collect in the niches & grooves of the HDD housing, so i suspect that it was the surface that reached up to touch the head rather than the other way round..

 

[de.das.dude]

the armature is not very powerful. however there are two super duper strong magnets as well.
so strong that you cant remove them by hand if they stick to something ferrous

 

[FordGT90Concept]

Programs like scan disk attempt to write a block of data to a sector then read it back. If the read back doesn't match what was written, it is marked as bad.

Bad sectors are caused by the platter failing to receive magnetization or have lost magnetization. Power flucuations could be blamed, as well as the motor not spinning fast enough or too slow (throwing everything off), the read/write head coming into contact with the platter, an electrical failure so the read/write head isn't where it thinks it is, or atomic degredation of the platter from years of fatigue.

 

[westom]

They can and do touch the platter if you throw it hard enough

Anything is possible in fiction and subjective reasoning. Put numbers to your claims. 60Gs. Good luck generating that kind of 'hard'.

Surges and excessive DC voltages are mostly based in myths. Most electrical failures are manufacturing defects. Most failures on disk drives electronics cannot happen without other damage that does not exist. With the number of possible failures inside a disk drive's computer (controller) board, it is rather amazing disk drives work at all.

Circuits required to exist in power supplies make overvoltages virtually impossible. Of course, that means a computer assembler who selected that supply has electrical knowledge. An A+ Certified computer tech needs no electrical knowledge to pass the tests.

Damage due to nearby magnetic fields is also a myth. As de.das.dude so accurately notes, two magnets more powerful than most anything you have handled are located adjacent to the disk platter. And cause no data destruction. Trivial magnetic fields outside the drive are destructive only in subjective reasoning.

Most every reason (electrical and mechanical) for drive failure is a manufacturing defect. At one point years ago, a Seagate factory completely shutdown for a long period due to too many manufacturing defects. To make working disk drives means an almost religious understanding of concepts taught by W E Deming. And by ignoring most of what is taught in business schools; that say failure is acceptable.

 

[twilyth]

Just as an aside, if you want to feel what a really strong magnet can do, search online for N45 Neodymium magnets. I think the rating goes up to N50, but those are really expensive. N45's aren't cheap but you can get a couple of 1/2" cubes for about $10-20. Don't get anything bigger because until you understand just how powerful these things are you could actually hurt yourself.

 

[Stevicus]

Just as an aside, if you want to feel what a really strong magnet can do, search online for N45 Neodymium magnets. I think the rating goes up to N50, but those are really expensive. N45's aren't cheap but you can get a couple of 1/2" cubes for about $10-20. Don't get anything bigger because until you understand just how powerful these things are you could actually hurt yourself.

So inside the drive its the potential of these 2 magnets that add & remove the data is it ?

 

[twilyth]

So inside the drive its the potential of these 2 magnets that add & remove the data is it ?

The magnets are used in positioning the arm that the read/write head rides on - aka the actuator. Honestly, I've never investigated how voice coil actuators work, so I looked it up. I hope this answers your question.

article

Hard drive manufacturers know it's OK to put magnets in a hard drive. Which is good, because no modern drive would work without one.

Old hard drives use stepper motors for their head positioning. Stepper motors rotate by one precisely defined small amount - one "step" - every time they're fed a current pulse. Which makes them a good way to make something like a hard drive read/write assembly move by the small steps needed to position it accurately over tracks on the drive.

Steppers are slow, though, and they're position-sensitive (the heads will end up in a slightly different place if the drive's tilted), and they're sensitive to temperature changes, and they wear out.

An alternative head motor design, which is used by all drives these days, is the voice coil. There's a coil next to a permanent magnet; when current's passed through the coil, it creates its own magnetic field, which interacts with the static field from the permanent magnet, and moves the head arm one way or the other depending on the direction of the current.

This motor design isn't at all precise, so there are "servo tracks" on the drive platters, which the heads read to allow the drive to tell where they are. That information lets the drive use a feedback mechanism to get very good precision. Presto, cheap super-high-track-density commodity hard drives.

Voice coil motors are better than steppers, because they have no temperature or position sensitivity to speak of, they're fast, there are no motor bearings to wear out, and they cost less.

The reason why these motors are called voice coils is that the early ones had the same straightforward cylindrical design as the voice coils in speakers. So that's the name they got. Then came various curved-magnet designs, but nowadays consumer drives all have simple swing-arm motor arrangements, with flat bent magnets that're magnetised lengthwise - with a pole at each end.

There's much, much more info at the link if you're interested.