Centos – Is mdadm Raid-1 Over A Network File Share Possible

While afs looks to be an obvious solution, I'd previously looked at this in some depth for a highly custom web application - and the fastest / most efficient / reliable solution was to implement to replication within the app - using rsync when bringing nodes back online. I did have a longer term plan to implement demand-based resynchronisations using inotify as the trigger (but never found the time).

As a solution, I was going to mount a RAM drive (tmpfs) that mirrors the GlusterFS web files but get the webserver to use the RAM drive

Yes, if GlusterFS does not support synchronization of cache invalidations, then it might be slightly faster (at the cost of not updating in real-time) although unless you have a very high data turnover, you'll probably find it faster to use a optimized file-system on a conventional device rather than a RAM drive.

You're probably going to see similar problems with any shared disk file systems (but this is mostly guesswork on my part).

A better solution would be to use a database (cluster?) to store any data - clustering is much more manageable (and easier to implement). See also mysql replication and Cassandra.

/me wonders if you could use overlay filesystems (unionfs) - putting the local copy on top and the remote system underneath then run rsync periodically from top to bottom - although I suspect it may prove difficult to delete files.

HTH

C.

If you write directly, it will not be replicated through glusterfs. If you read directly, you run the risk of your repair not working correctly if your drive fails. When you read a file, it checks the metadata, and if the file doesn't exist locally, replicates it rather than replicating the filesystem when the drive is brought online.

If those files are created regularly, can you write them to a non-distributed mount and use that for the files?

You can do what you want, but, it'll probably break in some very odd ways. One scenario would be if you modify a file on one node, the other node wouldn't know that the metadata changed and would read the old file. You might stop by the GlusterFS mailing list, they are extremely helpful.