Basic User Manual
1.0 About Legion
Developed at the University of Virginia, Legion is an integrated software system for distributed parallel computation. While fully supporting existing codes written in MPI and PVM, Legion provides features and services that allow users to take advantage of much larger, more complex resource pools. With Legion, for example, a user can easily run a computation on a supercomputer at a national center while dynamically visualizing the results on a local machine. As another example, Legion makes it trivial to schedule and run a large parameter space study on several workstation farms simultaneously. Legion permits computational scientists to use cycles wherever they are, allowing bigger jobs to run in shorter times through higher degrees of parallelization.
Key capabilities include the following:
- Legion eliminates the need to move and install binaries manually on multiple platforms. After Legion schedules a set of tasks over multiple remote machines, it automatically transfers the appropriate binaries to each host. A single job can run on multiple heterogeneous architectures simultaneously; Legion will ensure that the right binaries go to each, and that it only schedules onto architectures for which it has binaries.
- Legion provides a virtual file system that spans all the machines in a Legion system. Input and output files can be seen by all the parts of a computation, even when the computation is split over multiple machines that don't share a common file system. Different users can also use the virtual file system to collaborate, sharing data files and even accessing the same running computations.
- Legion's object-based architecture dramatically simplifies building add-on tools for tasks such as visualization, application steering, load monitoring, and job migration.
- Legion provides optional privacy and integrity of communications for applications distributed over public networks. Multiple users in a Legion system are protected from one another.
These features also make Legion attractive to administrators looking for ways to increase and simplify the use of shared high-performance machines. The Legion implementation emphasizes extensibility, and multiple policies for resource use can be embedded in a single Legion system that spans multiple resources or even administrative domains.
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