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HDFS >> mail # dev >> Secure deletion of blocks

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Re: Secure deletion of blocks
Just to clarify, ext4 has the option to turn off journalling.  ext3 does
not.  Not sure about reiser.

On Tue, Aug 20, 2013 at 12:42 PM, Colin McCabe <[EMAIL PROTECTED]>wrote:

> > If I've got the right idea about this at all?
> From the man page for wipe(1);
> "Journaling filesystems (such as Ext3 or ReiserFS) are now being used by
> default by most Linux distributions. No secure deletion program that does
> filesystem-level calls can sanitize files on such filesystems, because
> sensitive data and metadata can be written to the journal, which cannot be
> readily accessed. Per-file secure deletion is better implemented in the
> operating system."
> You might be able to work around this by turning off the journal on these
> filesystems.  But even then, you've got issues like the drive remapping bad
> sectors (and leaving around the old ones), flash firmware that is unable to
> erase less than an erase block, etc.
> The simplest solution is probably just to use full-disk encryption.  Then
> you don't need any code changes at all.
> Doing something like invoking shred on the block files could improve
> security somewhat, but it's not going to work all the time.
> Colin
> On Thu, Aug 15, 2013 at 5:31 AM, Matt Fellows <
>> Hi,
>> I'm looking into writing a patch for HDFS which will provide a new method
>> within HDFS which can securely delete the contents of a block on all the
>> nodes upon which it exists. By securely delete I mean, overwrite with
>> 1's/0's/random data cyclically such that the data could not be recovered
>> forensically.
>> I'm not currently aware of any existing code / methods which provide
>> this, so was going to implement this myself.
>> I figured the DataNode.java was probably the place to start looking into
>> how this could be done, so I've read the source for this, but it's not
>> really enlightened me a massive amount.
>> I'm assuming I need to tell the NameServer that all DataNodes with a
>> particular block id would be required to be deleted, then as each DataNode
>> calls home, the DataNode would be instructed to securely delete the
>> relevant block, and it would oblige.
>> Unfortunately I have no idea where to begin and was looking for some
>> pointers?
>> I guess specifically I'd like to know:
>> 1. Where the hdfs CLI commands are implemented
>> 2. How a DataNode identifies a block / how a NameServer could inform a
>> DataNode to delete a block
>> 3. Where the existing "delete" is implemented so I can make sure my
>> secure delete makes use of it after successfully blanking the block contents
>> 4. If I've got the right idea about this at all?
>> Kind regards,
>> Matt Fellows
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