Active Synchronization Across a Network?
June 15, 2009 12:09 PM   Subscribe

I need a lightweight program that can actively synchronize files across a network.

I am looking for something like Dropbox that can actively monitor when a file is changed and synchronize it across a network. I have no trouble finding programs like Microsoft's SyncToy, but this requires running a synchronization operation, which has to be scheduled.

I really like Dropbox, but its space limits along with the need to upload a modified file to their server and then subsequently download the file on the other networked computers have me looking for something else.
posted by sciencemandan to Computers & Internet (13 answers total) 2 users marked this as a favorite
You're probably looking for Unison
posted by iamabot at 12:20 PM on June 15, 2009

Response by poster: Thanks for your response, iamabot, but Unison doesn't do the active file monitoring. That's a dealbreaker for me.

See also this similar previous question that doesn't seem to have been answered. That is exactly what I am looking for.
posted by sciencemandan at 12:27 PM on June 15, 2009

Which OS? Windows?
posted by chrismear at 12:47 PM on June 15, 2009

how about a virtual drive "in the cloud" ?
posted by Baud at 1:04 PM on June 15, 2009

There is no such thing as active file monitoring, a program has to manually poll directory contents/files for changes. Just run Unison on a scheduled task and you should be set.
posted by wongcorgi at 1:49 PM on June 15, 2009

FileHamster will monitor folders or individuals files and quietly make a backup in a place you specify, which can be local or on a network or removable drive. This probably isn't what you want, though, as the backup folder isn't a mirror of your source, but more of a revision dump; however, FileHamster is free and might offer something that you like.
posted by 4eyes at 2:07 PM on June 15, 2009

There is no such thing as active file monitoring, a program has to manually poll directory contents/files for changes

This isn't true, at least on Windows. The operating system can provide filesystem notifications to programs, which are fired whenever a file is created, renamed, changed, deleted etc. Windows is handling these operations in the first place, so it's easy for it to notify programs without requiring any polling. In .NET , the FileSystemWatcher class does this.

I don't know offhand if any sync programs take advantage of this, or if they all just poll.
posted by matthewr at 2:14 PM on June 15, 2009

I use Windows Live Mesh ( They offer 5GB of free storage online for anything synchronized, but they also do p2p synchronization between computers for unlimited sizes. I use it to replicate my music/photos/portable-apps from home to work, and on various laptops. It's an app that runs in the background and does everything in real time.
posted by blue_beetle at 2:52 PM on June 15, 2009

Note, wongcorgi is wrong.
posted by Good Brain at 3:11 PM on June 15, 2009

Does Windows Live Sync do what you want? It appears to use peer-to-peer syncing, so may not have the file limits that Live Mesh has.
posted by seanyboy at 4:37 PM on June 15, 2009

Actually - It looks like it does do what you want. Here's some more information.
posted by seanyboy at 4:39 PM on June 15, 2009

Dropbox definitely does "active" file monitoring. There are APIs available on all three major platforms that allow this.

As for Dropbox, their next release is supposed to include LAN P2P sync, which eliminates redundant downloads over the network, so that would resolve one of your issues with Dropbox. According to that announcement, that feature was expected within 2-3 months as of April 11.

Here is a similar Ask Mefi thread that wound up recommending something called CrashPlan.

I don't think that running Unison on a very frequent schedule is necessarily such a bad idea, either. Contrary to that other thread, it doesn't need to scan every file each time to see if it's changed; it will use timestamps/metadata if you set it that way (it's the default, I think), and it also won't pull a file across a network just to checksum it (it will checksum on the remote side). Basically, a Unison run where very few files have changed should be very lightweight, both in terms of CPU and network bandwidth. I bet you could even get away with running it once per minute, and do you really need changes to show up faster than that?

Finally, I seem to remember hearing at some point that Dropbox had some plans to release a standalone/LAN-based version of their software, so obviously if that ever happened you would be set.
posted by dixie flatline at 9:00 PM on June 15, 2009

Oops, this is the correct link to the Dropbox announcement.
posted by dixie flatline at 9:03 PM on June 15, 2009

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