Q: How much does platter alignment matter?

Discussion in 'SSDs & Data Storage' started by botboy, Jul 12, 2005.

  1. botboy

    botboy 2[H]4U

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    Ok, so long story short I was in a car accident and my 250 gig WD drive was on the passenger floor, took a significant shock and now it makes bad bearing noise as it starts up and powers down as the bearing driver chip gets really hot.

    Now I popped open the drive, there aren't any scratches on the platters themselves (I'm assuming the head was towards the front during the accident). As I *stupidly* don't have a couple backups of some important things, I'm wondering if I can swap the platters over to an identical drive and have it work, or will the alignment between the three platters make this impossible? Has anyone tried this before?
     
  2. DougLite

    DougLite [H]ardness Supreme

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    You have already ruined the drive and platters. Opening the cover on a drive with a platter density of more than 20GB will toast it instantly, even if you take precautions against dust or other particles entering the enclosure. The tracks are simply packed too tightly together for the actuator to pick them back up after the enclosure has been opened. At this juncture, your only hope is a professional data recovery company. Seagate DRS will look at the drive for free, but recovery will be north of $1000 to get anything back.

    Even a speck of dust that is not visible to the naked eye can wreck a hard drive. There's no way the platters will ever be read in a drive again.
     
  3. QwertyJuan

    QwertyJuan [H]ardForum Junkie

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    exactly what were you thinking?? lol...

    QJ
     
  4. perplex

    perplex Gawd

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    if it started making noise why didn't you back everything important (to you) up quickly as possible then buy another drive? :confused:

    atleast you learnt the hard way why you should backup data always. i still have to learn my lesson because i have a deathstar running for 5 years here :p
     
  5. QwertyJuan

    QwertyJuan [H]ardForum Junkie

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    I had a friend that actually hooked up an LED somehow to the platter on his and plugged it in and turned out the lights... it made for a cool show anyhow!! :D

    QJ
     
  6. altec

    altec [H]ard|Gawd

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    I could make a funny joke from that post.
     
  7. botboy

    botboy 2[H]4U

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    I think I was thinking don't hit the truck, don't hit the truck, don't hit the truck and then there was this big SMACK as my '90 maxima rearended an F-150. Did you even read my fucking post?

    The drive was toast the second I hit that truck, but I popped the cover off out of curiosity, and nobody has answered my question.
     
  8. UICompE02

    UICompE02 SCSI Master

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    I think the answer is that alignment wouldn't matter at this point because popping the cover of the drive open would have introduced enough foreign matter that no drive head would be able to read from the platters without destroying them or the read/write head.

    Have you ever seen those diagrams that show how closely a drive head floats next to a drive platter in a modern drive? Even a particle of cigarette smoke is bigger than the gap. I'd say the drive is a lost cause without some very expensive professional recovery.
     
  9. UICompE02

    UICompE02 SCSI Master

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    Be careful here... I think he was referring to you opening the drive cover, not what were you thinking when you hit the truck...
     
  10. QwertyJuan

    QwertyJuan [H]ardForum Junkie

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    LOL exactly...

    QJ
     
  11. botboy

    botboy 2[H]4U

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    The drive was toast anyway, so that point is moot. If the drive was already dead, I didn't kill it any more by popping the cover off.

    Now, I am *still* curious tho, do drives assume that the platter is completely fixed, or do the read/write heads look for an alignment byte on each individual platter when the drive starts?
     
  12. DougLite

    DougLite [H]ardness Supreme

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    I also said the platters are toast. The tolerances are too tight on a drive of 80GB platter density for them to be relocated from one to another, even if you did have a clean room. The drive would have to be literally re-assembled from square one at the factory with your existing platters in order for it to be ready again. Perhaps I was not clear enough the first time - you will NOT recover any of the data on those platters. As a matter of fact, putting the platters back in would probably cause a head crash and permanently damage the platters if you gave power to the motor. Once again, ANY changes to the location of the disks relative to the heads will make the drive inoperable. In conclusion, yes you are hosed. Contact Seagate DRS and see what they say about the cost of pro recovery.
     
  13. hacktor2

    hacktor2 Limp Gawd

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    The harddrive platter isn't super rigid, when spinning it fluctuates like a wave, and the harddrive suspension compinsates for this and it still keeps the read/write head extremely close to the platter.
     
  14. StorageJoe

    StorageJoe Limp Gawd

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    Reason being..... the platter isn't perfectly round. It's kinda egg shaped due to manufacturing tolerances (more so on non enterprise drives). If it were very rigid you wouldn't be able to read or write any data. The vibration would not allow the head to follow (or even find) the track.
     
  15. Ice Czar

    Ice Czar Inscrutable

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    ^ 2 microns is a typical fly height

    and a human hair is about 76 microns
    the head running over even a smoke particle has been described as running over a bowling ball in a go cart at mach 813
    (10k rpm)

    hacktor2 has addressed the third dimension, & prior to startup the heads are parked as they will immediately park with a power loss, the heads actually "float" on air and its why drives arent rated for high altitude use as the air density deceases too much for reliable operation (and why you dont cover that little hole in the drive top)
    http://www.pcguide.com/ref/hdd/op/actParking-c.html
    Im not positive but Id guess that with modern densities the IBM load\unload scheme has been widely adopted and physical conatct even in the parking zone no longer occurs

    as far as the 2 dimensions go servo bursts are distributed throughout the platter
    http://www.lostcircuits.com/hdd/hdd2/3.shtml

    platter flex is a big issue and is what has driven smaller and smaller platter size adoption
    the smaller tha platter the less flex the higher the speed and the more resistance to impact, (why you dint see 3.5" form factor drives in laptops) & taken to an extreme with a microdrive
    http://www.pcguide.com/ref/hdd/op/mediaSize-c.html


    >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

    supplemental regarding altitude

    http://www.pcguide.com/ref/hdd/perf/qual/spec-c.html
    The only caveat about applying the power supply environmental specifications here is that hard drives are more sensitive to altitude than most components and can fail when operated at altitudes over 10,000 feet; >

    Floating Height / Flying Height / Head Gap
     
  16. QwertyJuan

    QwertyJuan [H]ardForum Junkie

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    ok then.... if the hole at the top sucks in air(i never really gave that a second thought b4) then why doesn't the dust get in on the platters??

    QJ
     
  17. DougLite

    DougLite [H]ardness Supreme

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    There's a super-duper filter on that hole. Kind of arcane/simplistic, but that's what they do. Trust me, only air gets in.
     
  18. QwertyJuan

    QwertyJuan [H]ardForum Junkie

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    Sounds reasonable! :)

    QJ