A Partial Zero Pass On Hard Drive?

Discussion in 'Mac Basics and Help' started by BikerJim, Jun 23, 2009.

  1. BikerJim macrumors newbie

    May 13, 2009
    Unfortunately I'm having to return my new Mac Pro, one month old. It has logic board problems. Kudos to Apple for their first suggestion,
    "Jim, would you like to exchange it for a new one?" "Heck yes!" I said.
    Anyway, I have 4 internal 1TB drives that I need to zero out. One zero pass on one drive takes 3+ hours. I would like to do a 7 pass on each drive, but that would take four days (90 hours) by my count before I could ship it back. And I want my new Mac asap!
    Question? The most each drive contained was 500GB's. Can I do a zero pass on a drive and stop it approximately halfway through (hit Skip button) and then repeat the (half) process over again as often as I desire. Will my half used drives and/or data be zeroed out multiple times.
    If so this would save me many hours of zeroing out half empty drives!
    Hope I made myself clear, if not, let me know, OK?

    Thanks for a great forum, Jim ;o)

    Edit; Man, do I ever get long winded sometimes!
    In short, what effect does a partial zero pass have on a hard drive?
  2. BlueRevolution macrumors 603


    Jul 26, 2004
    Montreal, QC
    A 7 pass erase will write over the entire drive 7 times, that is, it will write over every sector on the drive, then return to the beginning and repeat. It does not overwrite each sector 7 times before moving on to the next. Therefore, if you stop erasing after 3 passes, the entire drive will have been overwritten 3 times, and your data will be roughly as secure as it would be if you'd run three 1-pass erases.

    I say "roughly" because they do use different algorithms to overwrite, but at the end of the day one completely-overwritten drive is much like another.

    So yes, you can stop (skip) whenever you need to.

    Oh, I see what you're saying. No, because drives are not always written sequentially beginning to end, you can't be certain that all data on a half-full drive will be erased after running half of one pass.
  3. BikerJim thread starter macrumors newbie

    May 13, 2009
    Thanks BlueR!
    I was afraid I'd get that answer.
    I can't afford (time-wise) to do 7 passes on all 4 drives,
    I think I'll just do 3 passes each and keep my fingers crossed.
    My drives should be fairly safe in Apple's hands, I hope.
    I wonder if they zero out returned good HDs before resale?

    Thanks again, Jim ;o)
  4. surflordca macrumors 6502a


    Nov 16, 2007
    Ontario, Canada
    I can't see :apple: wasting time doing that. They will just reformat and reinstall the OS. The other 3 drives they will just reformat...
  5. BlueRevolution macrumors 603


    Jul 26, 2004
    Montreal, QC
    I can't see Apple not observing basic privacy standards. I wouldn't want to get a drive with someone else's data on any more than I'd want someone else to have mine.
  6. Objectivist-C macrumors 6502

    Jul 1, 2006
    Anything more than a single pass is an utter waste of time on a modern drive.
  7. BikerJim thread starter macrumors newbie

    May 13, 2009
    Each contact with Apple, regarding my return, I'm more impressed. My last call I found out that when they get a returned HD they zero it out and then it's resold as a refurbished drive, either in a refurbished machine or as a single unit. It's good to have some confidence in a company now days!

    I'm curious about your comment "an utter waste of time on a modern drive." Why is this so? What I've read lately is that even a 7 pass is recoverable with some really sophisticated software programs. And it is possible for a amateur geek to eat through a single pass to retrieve private info.

    ;o) Jim
  8. ElectricSheep macrumors 6502


    Feb 18, 2004
    Wilmington, DE
    I don't know where you read that, but its utter nonsense. Assuming that a zero was actually written to the disk, there is no software in existence that can hope to recover the data.

    Reading data that has been written over on a modern hard drive requires highly specialized equipment which is very, very expensive.
  9. memco macrumors 6502

    May 1, 2008
    Anywhere from 1-3 passes should be plenty especially if Apple is going to do it once more when they get it. Hard drives are so dense these days that it is very very difficult to get at the data after it's been overwritten once.
  10. BikerJim thread starter macrumors newbie

    May 13, 2009
    Thanks memco,
    Just out of curiosity what do you mean by "hard drives are dense"?
    Apparently hard drives aren't the only things that are dense these days,
    e.g. BikerJim :confused:
  11. patrick0brien macrumors 68040


    Oct 24, 2002
    The West Loop

    This is a great question. Memco is exactly right. We've been dealing with 3.5" platters for year now, but we've been adding more and more capacity to them. Think of the drive platter (in industry parlance it's called, originally the 'Disk'), as something loaded with little grains. Each grain is a part of a group of grains that can hold a magnetic field, and that group can be either magnetized, or demagnetized. Well, as drives have progressed the size of the grains, and the size of the group of grains that hold the magetism has shrunk, so we could pack more and more onto the disk. So, the density has indeed been going up.

    Storage, in a raw sense is measured by Gb/in2 (Gigabits/Square Inch)

    Bit more history: A little while ago, the groups of grais were getting so small, they had to be 'stood up' to continue to function, while adding even more density.

    Here's an animation that I feel explains it well:Linkypoo

    So once zeros are written to the sectors (or bits), when they are this small, and dense, it's really hard to get any history that means anything.

    One pass is plenty anymore.
  12. BikerJim thread starter macrumors newbie

    May 13, 2009
    patrickO -
    Thanks for taking the time to explain the term "dense", without using my name ;o).
    I understand the concept now, and the video helped a lot.
    Tho I felt like I was 12 again, watching it made me smile.

    Thanks, Jim
  13. emt1 macrumors 65816

    Jan 30, 2008
    Data has never been recovered after a single zero-pass. Some claim that it's possible in theory though. Just do one pass and move on with your life.

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