Hi Lars, Yes, that is true. I also came to know about it few days ago that data is present in Memory(rather than persistent storage) of 3 DataNode if the replication factor is 3. In case of disaster like entire data center failure there might be some data loss. But these kinds of disaster are very rare at Enterprise clusters.(I am only worried about data loss in prod) In a normal failure of 1-2 node in cluster we would not loose any data due to WAL. The probability of data loss increases by a large amount when WAL is off. Is there any JIRA in HBase for utilizing HDFS-744? It would be great to have this feature in HBase.
Thanks, Anil Gupta On Thu, Jan 10, 2013 at 7:54 PM, lars hofhansl <[email protected]> wrote: > Not entirely true, though. > Data is not sync'ed to disk, but only distributed to all HDFS replicas. > During a power outage event across all HDFS failure zones (such as a data > center) you can lose data. > > > -- Lars > > > > ----- Original Message ----- > From: anil gupta <[email protected]> > To: [email protected] > Cc: > Sent: Thursday, January 10, 2013 2:38 PM > Subject: Re: persistence in Hbase > > Hi Mohammad, > > If the Write Ahead Log(WAL) is "turned on" then in **NO** case data should > be lost. HBase is strongly-consistent. If you know of any case when WAL is > turned on and data is lost then IMO that's a Critical bug in HBase. > > Thanks, > Anil Gupta > > On Thu, Jan 10, 2013 at 7:37 AM, Mohit Anchlia <[email protected] > >wrote: > > > Data also gets written in WAL. See: > > > > http://hbase.apache.org/book/perf.writing.html > > > > On Thu, Jan 10, 2013 at 7:36 AM, ramkrishna vasudevan < > > [email protected]> wrote: > > > > > Yes definitely you will get back the data. > > > > > > Please read the HBase Book that explains things in detail. > > > http://hbase.apache.org/book.html. > > > > > > Regards > > > Ram > > > > > > > > > On Thu, Jan 10, 2013 at 8:48 PM, Panshul Gupta <[email protected]> > > > wrote: > > > > > > > Hello, > > > > > > > > I was wondering if it is possible that I have data stored in Hbase > > tables > > > > on my 10 node cluster. I switch off (power down) my cluster. When I > > power > > > > up my cluster again, and run the HDFS and hadoop daemons, will the > > Hbase > > > > have my old data persisted in the form I left it?? or will I have to > re > > > > import all the data?? > > > > > > > > Thankyou for the help. > > > > > > > > -- > > > > Regards, > > > > Panshul. > > > > http://about.me/panshulgupta > > > > > > > > > > > > > -- > Thanks & Regards, > Anil Gupta > > -- Thanks & Regards, Anil Gupta
