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


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Secure deletion of blocks
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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