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HDFS, mail # dev - Some questions about BackupNode and AvatarNode.


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Some questions about BackupNode and AvatarNode.
André Oriani 2011-06-15, 04:14
Hi,

I've playing around HDFS code, trying to do something like Avatar Nodes but
using the backup node.  I have modified datanodes to forward heartbeats,
block reports  and block received to backup node . So those are my
questions:

1) Until now I did not force the BackupNode to stay on safe mode. So as the
first blocks were written ( using the namenode), the backup node told the
datanode to delete them. Why did it happened ? If I put it on safe mode  it
would not happen, right? Does putting the backup node in safe mode prevent
it from sending any commands that would contradict namenode and corrupt
data?

2) In the avatar node  solution, the blockReceived method returns a list of
blocks that the avatar datanode should retry to send to the namenode. Why is
it necessary?

3) If a client connects to the backup node,  can it perform any actions it
would perform if it were a namenode ?

Thanks for your time and regards,
André Oriani