Slashdot Mirror
Laptop/Server Data Synchronization?
gbr writes "I've been trying to automatically synchronize data between a laptop and a server. When the laptop is connected to the network, I want all writes to automatically propagate across to the server. When the laptop is disconnected I want the laptop user to continue working with the local data. When the laptop is reconnected, I want the data to automatically re-sync.
The issue is, the data on the server may have changed as well, which needs to propagate back to the laptop. The data doesn't contain anything too special, no database tables etc. It does contain binary data such as executables and word processing documents. I've looked at ChironFS, Unison file sync, and drbd. ChironFS needs a manual rebuild if a connection fails, and the user needs to know which machine contains the correct data. Unison requires the user to initiate the synchronization process manually every time, and drbd is just not meant for the job at hand. How do you automatically, and invisibly to the user (except in the case of conflicts), synchronize between a laptop and a server?"
I do this often and rsync is wonderful for such a task.
I have OSX laptops using portable home directories to do exactly what you are asking for.. a network home directory that is automagically sync'd to my laptop (thus making it portable). It works both ways, and I'm definitely happy with it. I'm not sure which OS you're using though. I wrote about how to do it in an article: Full Stack: Portable Home Directory over NFS on OSX authenticated via OpenLDAP on Debian Linux if you're interested. I also just got everything to work over AFP to an OSX server running open directory as well.. but haven't had time to write it up yet (btw, a lot fewer steps).
A great solution till it breaks... believe me it does break and when it does be prepared for heartache. There are ways to recover it, but I think it assumes to much and the potential to screw up is a big risk. There were several users at my place of employment that found out this the hard way and now we ban the usage of it. It's not so much finding the best tool, but managing the process overall and how to do that.. Well we are still in the process of developing that one!
# cat
Damn, my RAM is full of cats. MEOW!!
A few people hit this one pretty well. rsync (and probably rsyncd).
:)
The more complex problem has been thrown at me a few times. What if it's not just one person?
Say you have a repository of data that a dozen people may be working in. When they're all network connected, they're all dealing with the same file pool. When they take their off-line copies with them (unplugged laptops on vacation), they all make changes to the same files. Maybe mine is a one line change. Maybe one guy copy&pasted the first 3 chapters from War And Peace into a comment somewhere in the middle. Maybe another developer did some very intellectual looking changes but hosed some major functionality.
When you start putting machines back on the network, who is right? The 6 guys who did real work are obviously right(ish), but they all made different changes. The very last change will end up being someone's 3 year old kid who was pounding on the keyboard right before daddy shut down the laptop, saving the new changes. Probably the last is the most recent, and right by most methods.
It's not a pretty picture, and requires some intelligence to sort out the mess.
The only "good" resolution I've found is to give logical authority to the changes. Bob is in charge of development. Any changes going into the development or production tree must clear him. He should be able to recognize that the 6 guys made changes, and diff them to come up with the common changes. The 3 chapters of war and peace go by the way side. And the guy with the 3 year old "developer" gets reprimanded.
In the end, a good revision system and good backups are needed too. Something will slip through the cracks, and you'll need to roll back to something you hope is good.
I take control over whatever I'm working on, so if I know I'll be working offline, I'll scp the data to my laptop, work on it on the road, and scp my changes up to the server when I'm done. Anyone else who may have worked in my project space in the duration should have known better.
Serious? Seriousness is well above my pay grade.
"s/h/it"
You may want to reevaluate your approach to political correctness.