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12.5. DFSA ? MFS ?

People often get confused about what exactly MFS and DFSA are. As discussed before in the howto MFS is the feature of openMosix that enables you access to remote filesystems as if those filesystems were locally mounted. They are mostly mounted on /mfs . A common misunderstanding is that you need MFS in order to have openMosix working, this is not true, however it can make things easier.

With DFSA enabled, system calls will be executed on the remote node withouth migrating the process back to it's home node. This behaviour (direct filesystem access) causes processes migratiing to the data and not the other way around (which is common). If DFSA is not enabled MfS is "just" a non-caching network-filesystem.

Very generally speaking, if you don't have DFSA turned on, each and every I/O will go to the home node for execution. With DFSA turned on, if the file happens to be residing on the node where the process finds itself then the I/O will happen locally.

A very common error is that people mix kernels with DFSA enabled and disabled. So one has to have a way to find out wether DFSA is actually enabled. This information can be obtained by typing

cat /proc/hpc/admin/version