New hardware provisioning doc, and updates to menus

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docs/hardware-provisioning.md

+---
+layout: global
+title: Hardware Provisioning
+---
+
+A common question received by Spark developers is how to configure hardware for it. While the right
+hardware will depend on the situation, we make the following recommendations.
+
+# Storage Systems
+
+Because most Spark jobs will likely have to read input data from an external storage system (e.g.
+the Hadoop File System, or HBase), it is important to place it **as close to this system as
+possible**. We recommend the following:
+
+* If at all possible, run Spark on the same nodes as HDFS. The simplest way is to set up a Spark
+[standalone mode cluster](spark-standalone.html) on the same nodes, and configure Spark and
+Hadoop's memory and CPU usage to avoid interference (for Hadoop, the relevant options are
+`mapred.child.java.opts` for the per-task memory and `mapred.tasktracker.map.tasks.maximum`
+and `mapred.tasktracker.reduce.tasks.maximum` for number of tasks). Alternatively, you can run
+Hadoop and Spark on a common cluster manager like [Mesos](running-on-mesos.html) or
+[Hadoop YARN](running-on-yarn.html).
+
+* If this is not possible, run Spark on different nodes in the same local-area network as HDFS.
+If your cluster spans multiple racks, include some Spark nodes on each rack.
+
+* For low-latency data stores like HBase, it may be preferrable to run computing jobs on different
+nodes than the storage system to avoid interference.
+
+# Local Disks
+
+While Spark can perform a lot of its computation in memory, it still uses local disks to store
+data that doesn't fit in RAM, as well as to preserve intermediate output between stages. We
+recommend having **4-8 disks** per node, configured _without_ RAID (just as separate mount points).
+In Linux, mount the disks with the [`noatime` option](http://www.centos.org/docs/5/html/Global_File_System/s2-manage-mountnoatime.html)
+to reduce unnecessary writes. In Spark, [configure](configuration.html) the `spark.local.dir`
+variable to be a comma-separated list of the local disks. If you are running HDFS, it's fine to
+use the same disks as HDFS.
+
+# Memory
+
+In general, Spark can run well with anywhere from **8 GB to hundreds of gigabytes** of memory per
+machine. In all cases, we recommend allocating only at most 75% of the memory for Spark; leave the
+rest for the operating system and buffer cache.
+
+How much memory you will need will depend on your application. To determine how much your
+application uses for a certain dataset size, load part of your dataset in a Spark RDD and use the
+Storage tab of Spark's monitoring UI (`http://<driver-node>:3030`) to see its size in memory.
+Note that memory usage is greatly affected by storage level and serialization format -- see
+the [tuning guide](tuning.html) for tips on how to reduce it.
+
+Finally, note that the Java VM does not always behave well with more than 200 GB of RAM. If you
+purchase machines with more RAM than this, you can run _multiple worker JVMs per node_. In
+Spark's [standalone mode](spark-standalone.html), you can set the number of workers per node
+with the `SPARK_WORKER_INSTANCES` variable in `conf/spark-env.sh`, and the number of cores
+per worker with `SPARK_WORKER_CORES`.
+
+# Network
+
+In our experience, when the data is in memory, a lot of Spark applications are network-bound.
+Using a **10 Gigabit** or higher network is the best way to make these applications faster.
+This is especially true for "distributed reduce" applications such as group-bys, reduce-bys, and
+SQL joins. In any given application, you can see how much data Spark shuffles across the network
+from the application's monitoring UI (`http://<driver-node>:3030`).
+
+# CPU Cores
+
+Spark scales well to tens of CPU cores per machine because it performes minimal sharing between
+threads. You should likely provision at least **8-16 cores** per machine. Depending on the CPU
+cost of your workload, you may also need more: once data is in memory, most applications are
+either CPU- or network-bound.