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Glusterfs is a very flexible and easy-to-use network filesystem that offers a load of must-have features, one of which is the clustering/mirroring of volumes/directories across multiple servers over TCP/IP.
Perhaps the most common and useful replication configuration one would want to set up would be a directory mirrored across two physical servers. The traditional and frankly rather primitive way of accomplishing this is with an rsync mirror. You run rsync as a cron job every few minutes and it will look at the differences between the local/remote copy of directories and update the files in question. While this method works reasonably well, there are a lot of things to set up and keep track of. You have to deal with at least 3 pieces of software: rsync, ssh/sshd and cron, and from a logical point of view, it is not a very transparent scheme at all.
A network filesystem like Glusterfs abstracts away these underlying concerns. By dealing with just a pair of configuration files (glusterfs.vol and glusterfsd.vol), you can setup different kinds of distributed configurations behind a directory mount. It can be as simple as a single directory export ala NFS, a 2-server mirror like the rsync method above (but considerably more elegant) or complex multiple server clusters with striping.
Below is the bare minimum configuration for a 2-server mirroring setup as of Glusterfs-2.0.4. For the sake of clarity, no performance tuning settings are shown. A more comprehensive version can be found at http://gluster.org/docs/index.php/Automatic_File_Replication_(Mirror)_across_Two_Storage_Servers
Fig. 1 glusterfsd.vol - configures what gets exported by the glusterfsd server
volume posix type storage/posix option directory /storagedir end-volume # posix-locks seems to be required in glusterfs-2.0.4 even # though docs claim that it is already activated in storage/posix volume brick type features/posix-locks subvolumes posix end-volume volume server type protocol/server option transport-type tcp subvolumes brick option auth.addr.brick.allow * end-volume
Fig. 2 glusterfs.vol - configures what is intended to be mounted as a glusterfs filesystem
volume remote type protocol/client option transport-type tcp option remote-host w.x.y.z # IP of remote server, e.g. the mirror option remote-subvolume brick end-volume # I opted to use storage/posix instead of protocol/client for # the local copy, if someone has a comment on this, please # email me at andy dot sy @ neotitans dot com volume posix type storage/posix option directory /storagedir end-volume volume local type features/posix-locks subvolumes posix end-volume volume replicate type cluster/replicate subvolumes local remote end-volume
© 2009 by Andy Sy
Web Development / Rich Internet Applications (RIA) Development
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