Why do you really want to switch the system where your precious data is lying and also all 10 nodes at a time. i am not really sure of data lost, many hase gave the answer on that prospect, but what i can say there may be data corruption if you don't follow the correct handling of the cluster. :) right..
∞ Shashwat Shriparv On Fri, Jan 11, 2013 at 9:52 AM, anil gupta <[email protected]> wrote: > Never mind i got the Jira: > https://issues.apache.org/jira/browse/HBASE-5954 > > On Thu, Jan 10, 2013 at 8:16 PM, anil gupta <[email protected]> wrote: > > > 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 > > > > > > -- > Thanks & Regards, > Anil Gupta >
