Hi,

I have 2 files servers and I need to keep a directory in each of them in active synchronization with
each other.

Eg) Server 1 has a directory called s1Dir
Server 2 has a directory called s2Dir

I need to keep those two directories mirrored.
The only thing I can think of is using rsync, and I suppose I could run rsync as a cron job to run every couple of seconds.

Is that the best way of doing things?

Is there a program daemon that I could run that would take care of this for me?

I'm concerened about rsync. What happens if someone is working on file1 in directory s1Dir and
someone else is working on file1 in directory s2Dir. That would cause some pretty huge problems, wouldn't it? I would need a locking mechanism to lock files, and rsync doesn't provide that (does it?).

Thanks!

There is no easy way to keep two actively read/write filesystems in sync.

There are ways, and they are very _hard_. There are networking schemes that will handle active/active r/w block devices (on which you lay a filesystem).

Is active/active r/w what you _really_ need? Can you get away with one machine r/w, and the other read-only for emergencies?

Unfortunately, no. It needs to be active/active.

Basically the two file servers are on the other side of the country from each other and there
is a vpn connection that puts them on the same network. The "managers" figure having just one
share on one of the servers will be two slow for the people on the other side of the country.

So they want to have both directories (i.e. servers) to be active.

If I understand the above response, rsync isn't the tool to accomplish this?

I am aware of some very expensive software that can do this, but I though perhaps there was
a slick tool in linux that would help me out with this.

Any thoughts?

Thanks.

There are.
NetBD and GFS either and/or both can get this done.

Observation: If having the share on both sides of the country is too slow, then having every write written to both sides of the country will be too slow. There is some smart caching and locking that alleviates this, but there is those pesky laws regarding the speed of light and the conservation of energy.

The smart caching does the best it can but remember the gain is lost because the normal file-system caching done locally by the nearest server has to be turned off.

After writing this I thought: . o O ( This could be done at the application layer )
Google netted this:
http://www.sambaxp.org/uploads/media...r_on_sles9.ogg
http://www.sambaxp.org/uploads/media...r_on_sles9.pdf

Volker Lendecke's presentation on HA clustering with samba at last years Samba eXPerience conference.

This would make a huge addition to the LQ wiki if you keep notes on how this progresses.

Thanks for the links dgar.
Interesting stuff on HA.

There's also device-mapper mirror which is quite configurable.