| Scyld ClusterWare HPC: Administrator's Guide | ||
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ROMIO is a high-performance, portable implementation of MPI-IO, the I/O chapter in MPI-2: Extensions to the Message Passing Interface, and is included in the Scyld ClusterWare distribution. ROMIO is optimized for noncontiguous access patterns, which are common in parallel applications. It has an optimized implementation of collective I/O, an important optimization in parallel I/O.
ROMIO gives you an abstraction layer on top of high performance input/output. The details for the file system may be implemented in various ways, but ROMIO prevents you from caring. Your binary code will run on an NFS file system here and a different file system there, without changing a line or recompiling. Although POSIX open(), read(), ... calls already do this, the virtual file system code to handle this abstraction is deep in the kernel.
You may need to use ROMIO to take advantage of new special and experimental file systems. It is easier and more portable to implement a ROMIO module for a new file system than a Linux-specific VFS kernel layer.
Since ROMIO is an abstraction layer, it has the freedom to be implemented arbitrarily. For example, it could be implemented on top of the POSIX Asynchronous and List I/O calls for real-time performance reasons. The end-user application is shielded from caring, and benefits from careful optimization of the I/O details by experts.
To use ROMIO on NFS, file locking with fcntl must work correctly on the NFS installation. First, since file locking is turned off by default, you need to turn on NFSv3 locking. See the Section called File Locking Over NFS. Now, to get the fcntl locks to work, you must mount the NFS file system with the noac option (no attribute caching). This is done by modifying the line for mounting /home in /etc/beowulf/fstab to look like the following:
$MASTER:/home /home nfs noac,nonfatal 0 0 |
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