On Tue, 16 Jun 2009 12:40:46 +0200
Renat Golubchyk <ragermany@gmx.net> wrote:

> Hi all!
> 
> Short:
> What is the best way to setup something similar to RAID 1 over a WAN?

...

> One purpose of the setup is to have data redundancy. Thus we have to
> ensure that the data is replicated in a timely manner. Replicating MySQL
> data is not difficult. The problem is the file system data like uploaded
> documents and pictures. We can monitor changes in the file system and
> initiate rsync to copy files over the network, but I think it's not a
> good solution. What we are after is a network equivalent of RAID 1.
> Are there any viable solutions that could work over a WAN?

If replication after file is completely hit the disk is not acceptable
either because files are quite large or have to be really synchronous
then I'll second DRBD-with-HA-cluster-fs suggestion.

Otherwise, if it's acceptable to have each file replicated as soon as
it's fully stored on one node and link between nodes isn't good enough
clustered fs High-Availability features might play against you, but I
don't think rsync (via some sort of cron) is a good idea here, anyway.

You'd be better off using in-kernel dnotify / inotify reactors and
a simple script to track IN_MODIFY and IN_CREATE events, replicating
path in question (possibly via some sort of delta-transfer) as soon as
it hits the fs.
I even remember seeing inotify-tracking binary to use with common shell
scripts, although I believe any dedicated non-bash-hack implementation
should be better suited for such task.

-- 
Mike Kazantsev // fraggod.net