Dear Wiki user, You have subscribed to a wiki page or wiki category on "Hadoop Wiki" for change notification.
The "FAQ" page has been changed by SomeOtherAccount: http://wiki.apache.org/hadoop/FAQ?action=diff&rev1=105&rev2=106 Comment: Adding NFS question * `mapred.child.java.opts = -Xmx1024m` == What kind of hardware scales best for Hadoop? == - The short answer is dual processor/dual core machines with 4-8GB of RAM using ECC memory. Machines should be moderately high-end commodity machines to be most cost-effective and typically cost 1/2 - 2/3 the cost of normal production application servers but are not desktop-class machines. This cost tends to be $2-5K. For a more detailed discussion, see MachineScaling page. + The short answer is dual processor/dual core machines with 4-8GB of RAM using ECC memory, depending upon workflow needs. Machines should be moderately high-end commodity machines to be most cost-effective and typically cost 1/2 - 2/3 the cost of normal production application servers but are not desktop-class machines. This cost tends to be $2-5K. For a more detailed discussion, see MachineScaling page. == I have a new node I want to add to a running Hadoop cluster; how do I start services on just one node? == This also applies to the case where a machine has crashed and rebooted, etc, and you need to get it to rejoin the cluster. You do not need to shutdown and/or restart the entire cluster in this case. @@ -86, +86 @@ * general is for people interested in the administrivia of Hadoop (e.g., new release discussion). * -user mailing lists are for people using the various components of the framework. For example, if you are writing a job and have a question on the MapReduce API, a posting to mapreduce-user would be appropriate. * -dev mailing lists are for people who are changing the source code of the framework. For example, if you are implementing a new file system and want to know about the FileSystem API, hdfs-dev would be the appropriate mailing list. + + == What does "NFS: Cannot create lock on (some dir)" mean? == + + This actually is not a problem with Hadoop, but represents a problem with the setup of the environment it is operating. + + + Usually, this error means that the NFS server to which the process is writing does not support file system locks. NFS prior to v4 requires a locking service daemon to run (typically rpc.lockd) in order to provide this functionality. NFSv4 has file system locks built into the protocol. + + In some (rarer) instances, it might represent a problem with certain Linux kernels that did not implement the flock() system call properly. + + It is highly recommended that the only NFS connection in a Hadoop setup be the place where the NameNode writes a secondary or tertiary copy of the fsimage and edits log. All other users of NFS are not recommended for optimal performance. = MapReduce = == Do I have to write my job in Java? ==
