Archive for January, 2009

Sysadmin: file and folder synchronisation

Technology Over the years I’ve struggled to keep my folder data synchronised between my various desktop and laptops.

Here I present the tools I’ve tried and what I’ve finally settled on as possibly the ultimate answer to the problem of synchronising files and folders across multiple computers:

Sync Files


I’ve tried rsync, which is a great Open Source tool to securely synchronise data either one-way or both-ways.
It’s very efficient with bandwidth as it only transfer blocks of data that have actually changed in a file instead of the whole file. It can tunnel traffic across SSH and I’ve got a few cronjobs set up between various servers to back-up files daily.

It’s only weaknesses are that:

  • Every time it runs, it needs to inspect all files on both sides to determine the changes, which is quite an expensive operation.
  • Setting up synchronisation between multiple copies of the data can be tricky: you need to sync your computers in pairs multiple times, which quickly becomes expensive and risky if you have the same copy across multiple computers.
  • It doesn’t necessarily detect that files are in use at the time of the sync, which could corrupt them.


It a folder synchronisation tool whose specific purpose is to address some of the shortcomings of rsync when synchronising folders between computers. It’s also a cross-platform Open Source tool that works on Linux, OS/X, Windows, etc.

Unison uses the efficient file transfer capabilities of rsync but it is better at detecting conflicts and it will give you a chance to decide which copy you want when a conflict is detected.

The issue though is that, like rsync, it needs to inspect all files to detect changes which prevents it from detecting and propagating updates as they happen.

The biggest issue with these synchronisation tools is that they tend to increase the risk of conflict because changes are only detected infrequently.


WinSCP Is an Open Source Windows GUI FTP utility that also allows you to synchonise folders between a local copy and a remote one on the FTP server.

It has conflict resolution and allows you to decide which copy to keep.

It’s great for what it does and allows you to keep a repository of your data in sync with your local copies but here again, WinSCP needs to go through each file to detect the differences and you need to sync manually each computer against the server, which is cumbersome and time consuming.

General Backup tools

There are lot more tools that fall into that category of backup utilities: they all keep a copy of your current data in an archive, on a separate disk or online. Some are great in that they allow you to access that data on the web (I use the excellent JungleDisk myself) but file synchronisation is not their purpose.

Now for some Captain Obvious recommendation: remember that file synchronisation is not a backup plan: you must have a separate process to keep read-only copies of your important data.
File synchronisation will update and delete files you modify across all your machines, clearly not what you want if you need to be able to recover them!

Revision Control Systems

Revision control software like cvs, subversion, git, etc are generally used to keep track of changes of source code files; however, they have also been used successfully to keep multiple copies of the same data in sync.
It’s actually exactly what I use for all my source code and associated files: I have a subversion server and I check-out copies of my software project folders on various computers.

After making changes on one computer, I commit the changes back to the server and update these changes on all other computers manually.

While great at keeping track of each version of your files and ideally suited to pure text documents like source code, using revision control systems have drawbacks that make them cumbersome for general data synchronisation:

  • you need to manually commit and update your local copies against the server.
  • not all of them are well suited to deal with binary files
  • when they work with binary files, they just copy the whole file when it changed, which is wasteful and inefficient.

Revision Control System are great for synchronising source code and configuration files but using them beyond that is rather cumbersome.

Complex setup

All of the above solutions also have a major drawback: getting them to work across the Internet requires complex setup involving firewall configurations, security logins, exchange of public encryption keys in some cases, etc.

All these are workable but don’t make for friendly and piece-of-mind setup.

What we want from data synchronisation

I don’t know about you but what I’m looking for in a synchronisation tool is pretty straightforward:

  • Being able to point to a folder on one computer and make it synchronise across one or multiple computers.
  • Detect and update the changed files transparently in the background without my intervention, as the changes happen.
  • Be smart about conflict detection and only ask me to make a decision if the case isn’t obvious to resolve.

Live Mesh folders

Enters Microsoft Live Mesh Folders, now in beta and available to the public. Live Mesh is meant to be Microsoft answer’s to synchronising information (note, I’m not saying data here) across computers, devices and the Internet.
While Live Mesh wants to be something a lot bigger than just synchronising folders, let’s just concentrate on that aspect of it.

Installing Live Mesh is pretty easy: you will need a Windows Live account to log-in but once this is done, it’s a small download and a short installation.

Once you’ve added your computer to your “Mesh” and are logged in you are ready to use Live Mesh:

  • You decide how the data is synchronised for each computer participating in your Mesh:
    you’re in charge of what gets copied where, so it’s easy to make large folders pair between say your laptop and work desktop and not your online Live Desktop (which has a 5GB limit) or your computer at home. You’re in control.
  • Files are automatically synchronised as they change across all computers that share the particular folder you’re working in.
    If the file is currently used, it won’t be synced before it is closed.
  • If the other computers are not available, the sync will automatically happen as they are up again.
  • There is no firewall setup: each computer knows how to contact the others and automatically -and uses- the appropriate network: transfers are local if the computers are on the same LAN or done across the Internet otherwise.
    All that without user intervention at all.
  • Whenever possible, data is exchanged in a P2P fashion where each device gets data from all the other devices it can see, making transfers quite efficient.
  • File transfers are encrypted so they should be pretty safe even when using unsafe public connections.
  • If you don’t want to allow sync, say you’re on a low-bandwidth dialup, you can work offline.
  • The Mesh Operating Environment (MOE) is pretty efficient at detecting changes to files. Unlike other systems, in most cases it doesn’t need to scan all files to find out which ones have been updated or deleted.

Some drawbacks

  • It’s not a final product, so there are some quirks and not all expected functionalities are there yet.
  • The Mesh Operating Environment (MOE) services can be pretty resource hungry, although, in fairness, it’s not too bad except that it slows down your computer’s responsiveness while it loads at boot time.
  • You can’t define patterns of files to exclude in your folder hierarchy.
    That can be a bit annoying if the software you use is often creating large backup files automatically (like CorelDraw does) or if there are sub folders you don’t need to take everywhere.
  • The initial sync process can take a long time if you have lots of files.
    A solution if you have large folders to sync is to copy them first manually on each computer and then force Live Mesh to use these specific folders: the folders will be merged together and the initial sync process will be a lot faster as very little data needs to be exchanged between computers.

Bear in mind that Live Mesh is currently early beta and that most of these drawback will surely be addressed in the next months.


I currently have more than 18GB representing about 20,000 files synchronised between 3 computers (work desktop, laptop and home desktop) using Live Mesh.

While not 100% there, Live Mesh Folder synchronisation is really close to the real thing: it’s transparent, efficient, easy to use and it just works as you would expect.

Now that Microsoft has released the Sync Framework to developers, I’m sure that other products will come on the market to further enhance data synchronisation in a more capable way.
In the meantime, Live Mesh has answered my needs so far.


3 comments January 19th, 2009

Sysadmin: Recovering deleted Windows partitions

TechnologyI made a mistake the other day: I wanted to delete the partition on an external drive and in my haste ended up deleting the partition of a local hard drive instead…

The good thing is when you delete a partition using the Windows Disk Management console it doesn’t actually delete your files, only the partition header.

Windows Disk Management Console

With NTFS files systems, there is a backup at the end of the partition. The problem is how do you recover it?

I first looked at the instructions from Microsoft knowledge base article kb245725, downloaded the low-level sector editor Dskprobe but was getting no-where with it.

Searching google brings you to the usual list of recovery software that you can’t be sure will actually do the job until you fork $$ for them.
I’ve got nothing against paying for software but I’ve been bitten by false promises before.

My search ended up with TestDisk an OpenSource utility to manipulate and recover partitions that works on almost all platforms.
The user interface is DOS only, so it’s not pretty, not point-and-click user friendly but it has a fair amount of options and after fiddling around with it for 10 minutes, I was able to simply recover the backup boot sector and tada! all my files were back!

TestDisk in action

So, some recommendations when recovering lost partitions:

  • Don’t panic! If you only deleted the partition (whichever type), chances are you’re likely to recover it or at least salvage the files.
  • Obviously, be careful not to write anything over them, like recreating partitions and a file system.
  • If you use a utility like TestDisk, don’t blindly follow the on-screen instructions. At first, it was telling me that I had 2 Linux partitions on the device (which used to be true) but it did not see the NTFS one. Then it thought I had a FAT partition only until I switched to the advanced options and inspected the boot partition.
    Just know enough about file systems to know what you’re looking for.
  • Low-level tools are not for everyone, so if you’re not comfortable using them, don’t tempt your luck and try a paid-for recovery tool with an easier interface.

If you use TestDisk and you manage to recover your files, don’t forget to donate to encourage Christophe GRENIER, the author.


4 comments January 8th, 2009

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