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Messing with DropBox

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DropBox icon DropBox is one of the more amazing software tools of the past years. It synchronises a folder from your hard drive to the web, giving you access to its contents from your web browser as well as letting you synchronise it to several machines. Bonus features include the ability to share files and folders with other DropBox users, creating public web links to your files or an automatic photo web site for your Pictures folder.

An amazing number of my friends have DropBox accounts already [if you don’t, consider using this referral link, so both you and me get some bonus extra storage] and rightly so, because it ‘just works’ for many things. The service is reasonably reliable, its speed is all right, its available not just on the Mac but also on Windows and Linux and it’s essentially effortless. Many others tried and failed at achieving the same.

Yes, there are shortcomings of DropBox such as a potential lack of privacy and its disrespect for metadata like extended attributes (to be solved with their currently-in-development 0.8 release, it seems), so you may have to be a little careful, but in general it just works.

An interesting question we asked ourselves is how DropBox handles file system peculiarities. The HFS+ file system in its usual incarnation is case insensitive and case preserving, normalising its file names to a decomposed forms [thus, somewhat confusingly, if you name a file with a composed name, e.g. ‘ü’ (U+FC) in the Finder and copy its name afterwards or have its name in a folder listing by the web server, you get a decomposed result ‘ü’ (U+75 U+308)], whereas the file systems on Linux (Ext-something?) seem to be case sensitive and normalisation agnostic. How will DropBox reconcile these worlds?

Like this, it seems:

DropBox on Linux

Here we see DropBox syncing the file with the composed umlaut and refusing to sync the one with the decomposed umlaut. It appears that they are working in normalisation form C. DropBox does sync both the lowercase and the uppercase umlaut. Of course I won’t be able to get both of those file on my HFS+ volume and a ‘case conflict’ is created by DropBox. In addition to that it seemed that trying to edit the case conflicted files leads to things becoming a bit messy. E.g. after editing on the Linux side which could in principle handle the case difference, I ended up with four files for some reason, all of which had lowercase names:

DropBox case conflicts seen in the Linux file browser.

It doesn’t look like you may lose data because of this, but it does look like things may become a bit messy. Luckily one doesn’t work with files whose names differ just in capitalisation outside geeky tests like this.

April 11, 2010, 18:19

Tagged as dropbox, file system, hfs.


Comment by Stefan: User icon

DropBox is brilliant, it’s a pity they don’t sell their product so you can run it on your own server.

April 11, 2010, 22:31

Comment by ssp: User icon

I guess if you’re keen enough to run stuff on your own server, you’ll be happy to use SFTP, rsync, whatever… anyway. So I can sort-of understand that there won’t be much money in that kind of offering for the DropBox people.

If you want some privacy, you can still consider placing an encrypted disk image into your DropBox, I suppose. Kills some of the elegance, and probably requires a (small) bit of discipline when using it, but apparently that’s workable.

Personally I just don’t upload my dangerous state secrets to the internet…

April 12, 2010, 16:21

Comment by Stefan: User icon

Of course you can launch your own DropBox clone, but that’s not the point. From my point of view the interesting thing about DropBox is the well designed interface of their beautiful client software!

Concerning the suggestion with an encrypted disk image: If I have a 2 gb encrypted disk image in my dropbox doesn’t this result in 2 gb upload everytime I change one byte?

April 14, 2010, 22:46

Comment by ssp: User icon

Concerning the suggestion with an encrypted disk image: If I have a 2 gb encrypted disk image in my dropbox doesn’t this result in 2 gb upload everytime I change one byte?

It’s not that bad. On the one hand you can create a ‘Bundle Image’. These are bundles which contain which contain 8MB ‘band’ files with the data. I suppose without them Time Machine would be completely unusable for people using File Vault. If you are happy with using hidutil on the command line you can shrink the band files down to 1MB each.

On the other hand – and more relevantly – DropBox should even work with one of the old-school disk images as it seems to do some clever diffing to determine which parts of the file have changed need to be uploaded to the server, thus reducing data transfers. Hence, it’d really only need to update the changed parts of the disk image, making this workable.

[I imagine this is quite clever as they seem to do this across users as well. So if person A already put some pirated MP3s in his DropBox and person B uploads identical files, doing so is essentially free for DropBox. But even if person B added cover art, the additional cost will be just for that. Seems like good thinking to me.]

April 14, 2010, 23:19

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