Modules and NFS for Xen

I’m just in the process of converting a multi-user system to a Xen DomU. It was running on a stand-alone Fedora Core 5 i386 system and I want to run it on a Fedora 7 DomU under a CentOS 5 Dom0 on an Opteron system.

The first stage of the conversion was to copy an image of the Fedora Core 5 system and make it a DomU under CentOS. I had some problems getting a Fedora Core 5 Xen kernel to boot so I installed a 64bit CentOS 5 kernel with the Fedora Core 5 user-space and surprisingly everything worked. I had expected to have problems with kernel modules, but everything just worked! I had expected that the 32bit modutils would be unable to load 64bit modules, but things just worked.

The first stage was to have the old server NFS export /home and have it mounted by the Xen DomU, this worked well for about a week. The next step was to move the data on to the new server. My first attempt was to have the Dom0 running the filesystems and NFS exporting them to the DomU but this caused an OpenOffice error “Error saving the document Name: General Error. General input/output error.“.

So having 32bit Fedora Core 5 with a 64bit Cent OS 5 kernel NFS mounting from a 32bit Fedora Core 5 system works well, while mounting from a 64bit Cent OS 5 system fails. If anything I would have expected better results from having the same version of the kernel on NFS client and server.

The next issue is whether a 64bit Fedora 7 system in a DomU can NFS mount the data from the Cent OS 5 kernel with Fedora Core 5 user-space. If not it’ll make testing the Fedora 7 upgrade significantly more painful than it might otherwise be.

If only we had a network filesystem for Unix that supported POSIX semantics.

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