Dear Steve, Thank you for your reply. I did worried about my email got lost, but I will wait for an answer longer next time, thank you for reminding me : )
I understand that if you have data replica = 3, the namenode will assign the blocks that way. However, I still have a question, if the data replica = 1, I just use it for testing to see how HDFS works, what is the policy to decide which datanode gets which block? Thank you so much! Boyu Zhang Ph. D. Student Computer and Information Sciences Department University of Delaware (210) 274-2104 [email protected] http://www.eecis.udel.edu/~bzhang -----Original Message----- From: Steve Loughran [mailto:[email protected]] Sent: Friday, July 24, 2009 7:09 AM To: [email protected] Subject: Re: Questions on How the Namenode Assign Blocks to Datanodes 1. dont panic if nobody replies to your message in an hour and resend. Hadoop developers/users are in many different timezones, and people often only look at this at odd times in the day. Its best to wait 24 hours before worrying if your email got lost 2. The namenode decides, usually two blocks to one rack, another block to a different rack. This is to save on datacentre backbone bandwidth, but isolate you from the loss of an entire rack (not so unusual once your rack is on shared DC power/PSUs). 3. There has been discussion on having plug-in policy here, but it would need to work with the load balancer, the code that balances blocks across machines in the background.
