-Tracking Replication errors
Brian Bockelman 2009-09-10, 02:27
We're going through a review of our usage of HDFS (it's a good thing!
- we're trying to get "official"). One reviewer asked a good question
that I don't know the answer too - could you help? To quote,
"What steps do you take to ensure the block rebalancing produces non-
corrupted files? Do you have to wait 2 weeks before you discover this?"
I believe the correct answer is:
When a block is replicated from one node to another, only the
resulting block size is checked. The checksums on the source and
destination are not compared. Therefore, if there's any corruption
that occurs, it would take until the next block verification to detect
If you look at TCP error rates and random memory corruptions, it
wouldn't be surprising to see silent errors in copying between nodes,
especially on multi-hundred-TB or PB scale installs.