You can copy data from any node, so if you can do it from multiple nodes
your performance would be better (although be sure not to overlap
files). The master node is updated once a the block is copied it
replication number of times. So if default replication is 3 then the 3
replicates must be active before the master is updated and the data
"appears" int the dfs.
How long the updates take to happen is a function of your server load
and network speed and file size. Generally it is fast.
So the process is the data is loaded into the dfs, replicates are
created, and the master node is updated. In terms of consistency, if
the data node crashes before the data is loaded then the data won't
appear in the dfs. If the name node crashes before it is updated but
all replicates are active, the data would appear once the name node has
been fixed and updated through block reports. If a single node crashes
that has a replicate once the namenode has been updated then the data
will be replicated from one of the other 2 replicates to another 3
system if available.
Dennis Kubes
Venkates .P.B. wrote:
Am I missing something very fundamental ? Can someone comment on these
queries ?
Thanks,
Venkates P B
On 8/1/07, Venkates .P.B. <[EMAIL PROTECTED]> wrote:
Few queries regarding the way data is loaded into HDFS.
-Is it a common practice to load the data into HDFS only through the
master node ? We are able to copy only around 35 logs (64K each) per minute
in a 2 slave configuration.
-We are concerned about time it would take to update filenames and block
maps in the master node when data is loaded from few/all the slave nodes.
Can anyone let me know how long generally it takes for this update to
happen.
And one more question, what if the node crashes soon after the data is
copied into one it. How is data consistency maintained here ?
Thanks in advance,
Venkates P B
