MacOS – File/Folder Bi-directional Sync

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I need a good bi-directional file/folder sync utility for my Mac running OS X El Capitan 10.11.5. I have tried some options but none seem to perform the tasks exactly that I need. What I need is this:

A utility that will update files and folder structure between my primary Mac HD and an NAS and it has to be bi-directional. The solutions I have tried so far either only update files in one direction or they will not update the folder structure between the two drives.
Automation as much as possible. I have reviewed a couple of utilities that claim the ability to do everything I need in #1 but will only work when launched manually.

The main utilities I have tried so far are Unison, rsync and the built in file merger capability of Mac OS X. Unison has not worked since I started setting it up. There seems to be a conflict between the type of NAS Unison needs to operate and how my NAS is set up. I have connected with afp which Unison does not recognize.

Rsync will update files if I run it twice, in two different directions. The problem with this approach is there is no analysis done by Rsync to determine which file version is the most recent.

The built in capability of Mac OS X to merge files has limited capability that works but it only works for files, not for folders.

I am basically looking for something similar to the offline file option available in Windows.

Thanks

Best Answer

Think about your exact requirements, and check whether they would also allow using a synchronization tool that is not file-oriented. Bittorrent Sync or its open source cousin SyncThing should fit your use case fine, if I imagine all your requirements correctly.

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MacOS – way to refresh a Finder file listing

Yes!

A simple AppleScript can instruct the Finder to tell its front window to update every item. Such an AppleScript can be saved as an Application and then dragged to the Finder toolbar to give you a refresh button.

The AppleScript you need is quite simple:

 tell application "Finder" to tell front window to update every item

Paste the above text in Script Editor (in the Utilities folder), then use Export -> Application. THAT executable should be dragged, with CommandOption, to the Finder toolbar (that is, the top bar, not the sidebar).

You can change the icon following this answer.

What are good bi-directional, real-time synchronization utilities between Mac local folder and web server

Unison is my go-to tool for a bi-directional file sync. (Mac binaries are available on a contributor's site.) I tend to think of it as a more interactive, configurable, and bi-directional version of rsync. Since it's a good *nix citizen, it can be automated via your favorite method. It's open-source and has ports to major OS platforms.

Unfortunately, Unison is no longer under active development, which may or may not be an issue for you. (I think the last time I used it was under 10.6.) But, it does fit your requirements nicely:

It handles bi-directional sync and works great on large files and data sets.
It can run in a completely automated way or interactively (where your review and confirm every change).
It runs over SSH.
GUI and CLI interfaces are available. (FWIW, the Mac GUI version, while nice/convenient, was always slightly flaky for me.)
Its end-user documentation is excellent and thorough.
It has configuration options for a multitude of use cases.
It has a design principle of leaving things in a Good State at all times, which makes it easier to recover should the connection be lost at any time.

And here's the main selling point for using it (for me, at least):

For remote SSH targets, it logs into the remote machine, runs a separate copy of Unison there to scan for changes, and then reconciles the state with your local machine to only transmit the bits (or bytes :-)) that differ, much like rsync does. This makes it very efficient with bandwidth, and it's also able to maintain caches of its file index on each side to make subsequent scans faster. For large data sets, this is a huge deal.

There are other Mac-specific tools for file synchronization, but, IIRC, they tend to assume that the filesystem is local, and are either very inefficient with bandwidth or very presumptuous about file "changes" (metadata, actual data) on large remote files / data sets.

Unison worked the way I needed it to, was reliable, and made me confident in using it due to its great documentation. Thank you, Benjamin C. Pierce!

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