It's interesting how much this sounds like NFS. NFS works great, and serves a fairly obvious use case, but obviously requires some working knowledge of Unix and ssh technologies etc. Smart Sync gives a one-click install and forget solution. It makes me wonder why it took so long for this to be made, and what other things we Unix-heads take for granted that could easily be ported and marketed to a wider audience.
This particular class of "solution" has existed at the enterprise level forever: it's called Hierarchical Storage Management.
Windows even has a built-in overlay icon for an "offline file"--i.e., a file that exists within an HSM storage hierarchy, where the only copy of the data is currently in a lower part of the hierarchy (e.g. on a tape), and accessing it will trigger a delayed retrieval.
Of course, your own computer probably doesn't have any "HSM storage hierarchies", so even on an enterprise workstation, your local files will likely never show that overlay. Instead, it's more a thing you'll see if you have a home dir stored on a SAN, consumed by your workstation over SMB. In that sense, it's sort of a feature in the same group as "quota management."
Then again, it's not like you'd never run into it outside of an enterprise context; if you downloaded an AWS S3 filesystem driver for Windows, for example, the proper indicator for "this file exists only in Glacier" would be that same overlay, because S3's use of Glacier is also Hierarchical Storage Management.
So, like NFS - what happens if your internet connection is interrupted while you're reading the file? What happens if another computer saves to the same file while you're reading it?
Dropbox has smart people and I'm sure they would have wanted a feature like this from day 1, so if they're introducing it, I'm sure they have good answers. I'm just curious what they are!
NFS will, depending on mount options, block forever or start returning errors if the connection is lost. It's not really suitable for non-LAN use for a number of reasons.
It also will let you overwrite or interleave files unless both sides use advisory locking.
Yup. We use NFS at scale at $dayjob (including across continents, which is sometimes exciting) and I'm pretty sure everyone wishes we had something with the simplicity of Dropbox.
I'm curious how Dropbox has made this safe to use for people who don't want to think about things like "close-to-open consistency" or "stale file handle".
one cool thing I've seen "Smart Sync" do...on OS X it seems to fill out the thumbnail cache for images that are "online only". This means you can see the preview for what an image looks like without forcing the client to download it.
Also local files behave exactly like other local files so in that case (the typical case) all that pain you feel with NFS/FUSE goes away
