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Zero is a cluster of 58 dual-processor quad core Intel Harpertown based servers. Each machine has eight cores and 8Gb of RAM. Twelve of the machines have NVidia Tesla C870 graphics cards but this model is now obsolete so they are not in use. They all run Linux.

Zero can only be accessed by sshing into the head node, whose external name is zero.ch.cam.ac.uk. All work is done from there; there is no need to log into compute nodes. Zero uses the local Admitto service, so you log in with the same password as on the workstations.

Homespace is on a disk array attached to the head node. The /home filesystem is 400Gb in size and has user quotas which are currently set to 10Gb soft limit with a hard limit of 15Gb. It is backed up nightly and two weeks of incrementals are kept. /home is shared to all nodes on the cluster's internal network, so your job sees the same home directory wherever it is on the machine. It's important to remember that from a compute job's point of view accessing this directory is extremely slow, especially if all the nodes are trying at once. Compute jobs should always write data to a local disk if possible, and copy it back to /home at the end.

There is also a shared scratch filesystem /sharedscratch in which you will have a directory. These are not backed up. They have a quota restriction of 250Gb soft limit and 300Gb hard limit, but it is expected that most people will stay well within that amount. They have the same speed issue as /home.

Each node also has a local /scratch filesystem on which the queueing system will create you a directory when you use the node. These filesystems are about 140Gb in size with no quota restriction and are the most appropriate place for your jobs to write temporary files during a run. They are local to each node and so considerably faster than the NFS-mounted /home and /sharedscratch. Please clean up files on /scratch when you are done with them; see the queueing documentation for how to find out which node's /scratch to look at. All of the node /scratch directories are accessible under /nodescratch on the head node. The system uses an automounter so the directories only appear when you try to access them. For example to see the /scratch from node compute-1-5 you need to type something like 'ls /nodescratch/compute-1-5'.

The following software is installed: Intel Fortran, Intel C, Intel Math Kernel Library, Portland Group Fortran and C compilers, GNU compilers, NAG Fortran compiler, FFTW library, OpenMPI. The head node also has other software, including popular editors, as it is intended for interactive work. If there is a package missing from the head node that you would like to use then please ask; it will probably be possible to install it provided it is a sensible size.

Like most local clusters zero has the modules environment to allow you to switch between different compilers and libraries. The default environment is set up with Intel compilers and OpenMPI. If you need to change this then use the module avail command to see what the other options are, and edit the version you want into your ~/.bash_profile file.

All compute jobs should be run through the queueing system as users cannot log directly into the nodes. The queueing system will run each job on a set of free compute nodes, copying the output back to a user-specified file at the end of the job. The queueing system is SLURM; this will be familiar to users of the other theory sector clusters, but please note that the available queues are not the same on every machine. Read the generic instructions for instructions on how to use Torque and Zero's queueing setup for details of the queue setup if you already know Torque. The queueing configuration is always provisional and suggestions for improvements are warmly welcomed. To run parallel jobs you will need to use the appropriate job launcher; see Zero's parallel documentation for details.

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