Realtime Filesystem Replication

Bill Moran wmoran at
Tue May 6 12:06:36 PDT 2003

YOU wrote:
> Thanks so far to the suggestions including rsync and unison. Both appear
> to be triggered upon a command line or user typed command. Is someone
> using a system that tracks the mtimes for files and updates without
> prompt? 

Are you sure you really need _realtime_?  That's a pretty tall order, and
I don't know of anything that can provide it.

OTOH, with rsync as a cron job, you can easily mirror a large amount of
data, say, every 5 minutes.  If a 5-minute lag in data replication is
acceptable, I would recommend using rsync instead of looking for something
more "real time".  I don't know if any true "real time" synchronizing

Let me ask you a few questions: 1. What is the maximum acceptable "lag" for
data replication?  2. How much data do you estimate there will be?  (both
megs and # of files) 3. How often do you estimate the data will change?

If 1 is longer than a few minutes, and 2 and 3 aren't terribly demanding,
rsync is probably the way to go.

On a related note: I had an idea that you should be able to create some
sort of network RAID using the new GEOM system.  Something that would allow
everything that was written to a local filsystem to also be mirrored via
NFS to another system.  I haven't had a chance to do anything more than
dream about it, though.

Bill Moran
Potential Technologies

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