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

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Re: Secure deletion of blocks
Hi Matt,

Here are some code pointers:

- When doing a file deletion, the NameNode turns the file into a set of
blocks that need to be deleted.
- When datanodes heartbeat in to the NN (see BPServiceActor#offerService),
the NN replies with blocks to be invalidated (see BlockCommand and
- The DN processes these invalidates in
BPServiceActor#processCommandFromActive (look for DNA_INVALIDATE again).
- The magic lines you're looking for are probably in
FsDatasetAsyncDiskService#run, since we delete blocks in the background

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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