Can we run the Apache webserver to serve files off a PVFS volume?
Sure you can! However, we recommend that you turn off the EnableSendfile option in httpd.conf before starting the web server. Alternatively, you could configure PVFS with the option -enable-kernel-sendfile. Passing this option to configure results in a pvfs2 kernel module that supports the sendfile callback. But we recommend that unless the files that are being served are large enough this may not be a good idea in terms of performance. Apache 2.x+ uses the sendfile system call that normally stages the file-data through the page-cache. On recent 2.6 kernels, this can be averted by providing a sendfile callback routine at the file-system. Consequently, this ensures that we don’t end up with stale or inconsistent cached data on such kernels. However, on older 2.4 kernels the sendfile system call streams the data through the page-cache and thus there is a real possibility of the data being served stale. Therefore users of the sendfile system call are warned to be wary of this detail.
