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Old 12-15-2012, 08:14 AM   #1
tyler811
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Default How many passes to wipe a hdd

How many passes of DBAN would good for wiping out a hdd to reinstall windows? The computers are donations that are wiped, windows reinstalled and given back out again to low income families. Our concern is we want to clear all the old information but DBAN can take 24 hours or to do a hdd with 8 passes.
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Old 12-15-2012, 08:24 AM   #2
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I think 3 passes would be DOD standard.
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Old 12-15-2012, 08:38 AM   #3
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Dban tells you for each method how many wipes are low, medium and high security. I also recall a whitepaper or something proving that two different method medium-level wipes is exponentially more effective than one high-level. Also, Dban is good but other wipers can do the job much quicker.
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Old 12-15-2012, 08:39 AM   #4
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A single zero wipe is enough to make the data irrecoverable by any commercial specialist company. For hardware storing military secrets they incinerate the disks.

You need only to do a single sweep of the disk setting it to zero. Anything else beyond is beyond anybody but spy agencies, but we have no evidence they can recover it either.
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Old 12-15-2012, 10:01 AM   #5
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Quote:
Originally Posted by tyler811 View Post
How many passes of DBAN would good for wiping out a hdd to reinstall windows? The computers are donations that are wiped, windows reinstalled and given back out again to low income families. Our concern is we want to clear all the old information but DBAN can take 24 hours or to do a hdd with 8 passes.
Frankly I would say 1 would be enough if you even need to go that far. That's enough to stop a normal person from casually attempting to recover data with off the shelf hardware and free software. The fact that you're donating them to low income families pretty much rules out them taking them to a data recovery service, right?
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Old 12-15-2012, 01:32 PM   #6
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Likely one format pass is all you really need, but here are two additional steps you can take:

download a linux LiveCD, any distro. launch it with a USB stick or burn it to an optical disc. Make sure the hard drive you want to wipe is the only hard drive connected.
Boot the LiveCD and launch terminal:

dd if=/dev/zero of=/dev/sda bs=1M

That will zero every single bit on the hard drive (will take a few hours)

If you want to be extra special cautious, then do this before you zero everything:

dd if=/dev/urandom of=/dev/sda2 bs=1M

That will put random math function data on the whole hard drive. That one is limited by single threaded CPU speed, so it can take a while (almost a day per TB). Then user the /dev/zero line after it to zero the drive.

Those are probably overkill, but if you want to be sure sure, there's an option.
I dont' know what DBAN does, but I imagine it does the same thing as the first line I listed (the /dev/zero line)
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Old 12-15-2012, 01:45 PM   #7
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Quote:
Originally Posted by Concillian View Post
Likely one format pass is all you really need, but here are two additional steps you can take:

download a linux LiveCD, any distro. launch it with a USB stick or burn it to an optical disc. Make sure the hard drive you want to wipe is the only hard drive connected.
Boot the LiveCD and launch terminal:

dd if=/dev/zero of=/dev/sda bs=1M

That will zero every single bit on the hard drive (will take a few hours)

If you want to be extra special cautious, then do this before you zero everything:

dd if=/dev/urandom of=/dev/sda2 bs=1M

That will put random math function data on the whole hard drive. That one is limited by single threaded CPU speed, so it can take a while (almost a day per TB). Then user the /dev/zero line after it to zero the drive.

Those are probably overkill, but if you want to be sure sure, there's an option.
I dont' know what DBAN does, but I imagine it does the same thing as the first line I listed (the /dev/zero line)
I can't remember if DBAN has an option for zeros or not. Its primary function is to overwrite the data pseudo-random numbers and patterns, more akin to the second option you provide only much simpler for non-Linux users.
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Old 12-15-2012, 01:58 PM   #8
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Never. datarecovery software can still see your files after 10 formats.... thx
Do you even understand the difference between a format and a multiple pass secure wipe?
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Old 12-15-2012, 02:21 PM   #9
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Never. datarecovery software can still see your files after 10 formats.... thx
A format isn't a wipe. A wipe zeroes out all data.


As mentioned, commercial data recovery software can't even get your data after one zero-out, and it's unlikely anyone will use higher tech recovery (like for forensics and stuff I guess) on your drive unless you did something terrible. But if you're going to spend the time wiping a drive, I say do 3 to be paranoid. 7 would take forever.
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Old 12-15-2012, 02:30 PM   #10
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the need for multiple passes came from back when hard drives used stepper motors to position on tracks and they never positioned in exactly the same way twice.

any modern hard drive is unrecoverable after one pass

for SSDs you of course need to use their secure erase function

Last edited by tynopik; 12-15-2012 at 02:34 PM.
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Old 12-15-2012, 03:06 PM   #11
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tweakboy has got to be some long-term, subtle troll or an idiot.
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Old 12-15-2012, 10:12 PM   #12
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I can say this. I have formatted my computer and recovered the files very easily. A single wipe is more than likely all you need to do.
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Old 12-16-2012, 05:24 AM   #13
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A single pass of zero's is enough, as getting any additional data of such a drive is so expensive, that for most data it's simply not worth it.

The only easily recoverable data will be in deactivated sectors. That's between 512 and 4096 Bytes of contiguous data for each reallocated sector.
If you worry about those, you should've used full disk encryption anyway.
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Old 12-16-2012, 06:36 AM   #14
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so I know wabout this,,,,,, the only way to really do it is put a magniet on top of the HD and boot up......
lol
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Old 12-16-2012, 06:59 AM   #15
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A single pass of zero's is enough, as getting any additional data of such a drive is so expensive, that for most data it's simply not worth it.

The only easily recoverable data will be in deactivated sectors. That's between 512 and 4096 Bytes of contiguous data for each reallocated sector.
There may also be data stored in the "host protected area"; most drives allow for part of the drive to be restricted - it won't show up on scans, and the space is not reported by the drive, so the OS/partition tools/wipe tools can't see it. However, it can be read. It's frequently used by OEMs to store recovery tools, but some rather poorly-designed tools have used it to store software licensing data, crypto keys, etc.

Commercial drive wiping tools have the ability to "sniff out" HPAs and wipe them, as well methods of dealing with reallocated sectors (usually by completing the wipe but not issuing a certificate of wiping for the drive).

Like SSDs, HDDs also support secure erasure - it just takes a few hours to run. However, secure erasure is difficult for many people, because most PC BIOSs automatically issue a "security freeze" during POST which blocks the secure erase function. Often, drives can only be secure erased after hot-plugging into a running system. Even, then there is limited secure erasure software available; and much of it is provided by OEMs and locked to their drives.

Last edited by Mark R; 12-16-2012 at 07:01 AM.
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Old 12-16-2012, 08:17 AM   #16
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Quote:
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Yes,,, and have owned a P5K since 2007. Secure erase all you want.

Back 10 years ago me and my dad started company harddrivedatasavers.com

so I know wabout this,,,,,, the only way to really do it is put a magniet on top of the HD and boot up......
That website doesn't exist...This guy has to be a troll. A "magniet" won't do anything to a modern unopened hard drive, and if you open it you may as well destroy the platter physically if you've gotten that far.
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Old 12-16-2012, 09:11 AM   #17
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Back 10 years ago me and my dad started company harddrivedatasavers.com
How long before you were out of business? 3 months? 6?
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Old 12-16-2012, 09:18 AM   #18
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I would do 1 pass of random data, but 0s or 1s are faster.
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Old 12-16-2012, 10:01 AM   #19
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Quote:
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Yes,,, and have owned a P5K since 2007.
Please elaborate on how owning an Asus P5K makes you an expert on data recovery.
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Old 12-16-2012, 12:38 PM   #20
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Quote:
Originally Posted by Coup27 View Post
Please elaborate on how owning an Asus P5K makes you an expert on data recovery.
He has ........ Here is the copy below
Quote:
Originally Posted by tweakboy View Post
..
......
so I know wabout this,,,,,, the only way to really do it is put a magniet on top of the HD and boot up......
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Old 12-16-2012, 03:27 PM   #21
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Unless there was valuable data stored on the drive (corporate financials, medical records, state secrets), then a single zero-wipe pass should be enough.

DBAN defaults to a 3-pass DoD wipe, but you can set it to just do a zero-wipe pass, and it goes much faster. The DOS tools on a bootable CD image supplied by Seagate and WD can write zeros too, and do it faster. But those tools may not be compatible with today's larger HDs.
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