question on write failure and commit in HDFS

[Yang <te...@gmail.com>]

I wonder what happens if a HDFS client writes to 3 replicas, but only one of
them succeeds, but the other 2 fail,
then the client considers the operation a failure, but what happens to the
successful block? if another client does a latter read, and
hit on the successful block, it could read out the result ? (which was
probably not correct)
it seems to create a completely consistent view, there would have to be
something like 2 phase commit protocol .

also, what is the granularity of HDFS replication? for example, if I keep
writing a long file onto hdfs, does the client finish flushing a 128MB
block, and then tries to
replicate it to all 3 replicas ? or is every byte immediately copied to 3
replicas?

Thanks
Yang