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Old 05-26-2008, 11:23 AM   #1
writedom
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shred entire device or partition , remove file system first?


If shredding an entire device or partition does the file system being used make a difference. Doesn't shred overwrite data in place?

If the file system does make a difference (on entire devices or partitions) what file system is best to use if none at all?
 
Old 05-26-2008, 11:35 AM   #2
tredegar
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Quote:
If shredding an entire device or partition does the file system being used make a difference.
No.
Quote:
Doesn't shred overwrite data in place?
shred writes random data several times. If you are shredding a partition or whole disk, it doesn't care what filesystem you used, because it will be turned into random, meaningless data. There won't even be a "filesystem" (of any sort) when shred has finished. So the filesystem doesn't matter.
 
Old 05-26-2008, 11:37 AM   #3
writedom
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That's what I thought.

thanks
 
Old 05-26-2008, 11:39 AM   #4
bigrigdriver
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The filesystem certainly does make a difference. See the shred man pages for discussion on which filesystems are least/most affected by shredding.

Quote:
CAUTION: Note that shred relies on a very important assumption: that the file system overwrites
data in place. This is the traditional way to do things, but many modern file system designs do
not satisfy this assumption. The following are examples of file systems on which shred is not
effective, or is not guaranteed to be effective in all file system modes:

* log-structured or journaled file systems, such as those supplied with AIX and Solaris (and JFS,
ReiserFS, XFS, Ext3, etc.)

* file systems that write redundant data and carry on even if some writes fail, such as RAID-based
file systems

* file systems that make snapshots, such as Network Appliance's NFS server

* file systems that cache in temporary locations, such as NFS version 3 clients

* compressed file systems

Last edited by bigrigdriver; 05-26-2008 at 11:41 AM.
 
Old 05-26-2008, 11:42 AM   #5
writedom
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I read the man but wouldn't that only apply to shredding individual files on a journaling file system and not entire devices / partitions?
 
Old 05-26-2008, 11:51 AM   #6
tredegar
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Quote:
wouldn't that only apply to shredding individual files on a journaling file system and not entire devices / partitions?
That's certainly how I understand it.
bigrigdriver can you tell us more?
 
Old 05-26-2008, 12:04 PM   #7
bigrigdriver
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Yep. My bad. But you could probably do the job a lot faster my simply using cfdisk /dev/sda (or whatever the device is) to delete the partition(s). Then Write the change to delete the partition table. You would have a very hard time finding any files on the disk then.

If you are extremely paranoid about anyone using very expensive, high powered equipment to recover files, then nothing works better than sulphuric acid.
 
Old 05-26-2008, 12:09 PM   #8
Emerson
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Quote:
Originally Posted by bigrigdriver View Post
But you could probably do the job a lot faster my simply using cfdisk /dev/sda (or whatever the device is) to delete the partition(s). Then Write the change to delete the partition table. You would have a very hard time finding any files on the disk then.
Nope, writing the partition table back effectively restores it with all files intact. A tool like testdisk does restore the partition table with ease and is included on many LiveCD-s, e. g. Knoppix.
 
Old 05-26-2008, 12:32 PM   #9
tredegar
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Quote:
If you are extremely paranoid ...then nothing works better than sulphuric acid.
"Fire" is easier to get hold of nowadays

I confess that dead or redundant (who wants a 512MB HDD nowadays?) disks I take apart. Well, I'm a hardware man at heart, and the insides are often interesting.
By the time I have fingerprints all over the platters and have rescued a few good fridge magnets, I defy anyone to get the data back

@writedom: It looks as though you can just shred the partition / disk, if you'd like it to be re-usable but otherwise unrecoverable.
 
  


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