On Mon, Aug 13, 2012 at 12:31 PM, Aji Janis <[email protected]> wrote:
> I am very new to Hadoop and Accumulo. I need some information on how data > is backed up or guaranteed against system failures (if it is).I am > considering setting up a Hadoop cluster consisting of 5 nodes where each > node has 3 internal hard drives. I understand HDFS has a configurable > redundancy feature but what happens if an entire drive crashes (physically) > for whatever reason? How does Hadoop recover, if it can, from this > situation? More specifically, I am assuming Accumulo uses HDFS redundancy > to make back ups of the data. > > One, is this assumption true? > Yes, Accumulo uses HDFS replication to preserve data in the presence of failures. HDFS stores N exact copies of each data block, with each copy being stored on a different server. If a drive crashes, HDFS notices that blocks are under-replicated, and copies those blocks to an available drive. Thus the data can survive N-1 simultaneous failures. > Two, if I had a copy of the hard drive and I duplicate that to a new drive > and pop it in where the old/crashed drive used to be would this work? > Since that drive's data would have been replicated to other drives, you should not need a copy of it. You should just be able to put in a fresh hard drive, and HDFS will start using it. Billie > > I apologize if this is a really stupid question. But I highly appreciate > any help, pointers and suggestions! Thanks in advance. >
