Sync folders on your Mac with an external disk

Sync folders on the Apple Mac's disk drive with folders on an external disk drive

If you have an external disk drive such as a USB disk or even a NAS (network attached storage) disk, there are many uses for it and, for example, you could sync folders on the Mac's disk with it. FreeFileSync can do the job.

Time Machine is useful for making backups and SuperDuper is useful for cloning the disk drive, but neither of them is useful if you have a shared disk drive, such as a NAS drive on the network.

A NAS drive could be used to provide shared files for several Macs and PCs, or it could be used to store music, photos and videos for streaming over the Wi-Fi network.

If you are running the latest version of OS X, you should find that NAS drives simply show up in Finder windows. There is a special area for them in the sidebar.

FreeFileSync - sync folders on the Mac

This one is listed in the Shared section of the Finder sidebar (bottom left corner in the screenshot above), and selecting it shows the folders on the NAS drive. On older versions of OS X you might find that you need go to the Go menu and select Connect to Server, then enter the NAS drive’s IP address to connect to it.

You can create folders on the NAS drive in the usual way and in the next screenshot a Documents folder and a Google Drive folder have been created.

FreeFileSync - sync folders on the Mac

This is so that I can sync these two folders on the Mac’s internal disk with the ones on the NAS disk. You can sync any folders and the ones you choose will be different to mine.

Go and download FreeFileSync, it is free open source software, and double click it to extract the contents from the zip file. The folder or the files can be copied to the Mac’s Applications folder.

Double click the FreeFileSync app and if it will not open (OS X can be configured only to open apps from the Mac app store in System Preferences), right click or Ctrl+click the file and select Open. It warns you that the app is from an unknown developer, but I have tried it and found it to be OK, so open it anyway.

FreeFileSync - sync folders on the Mac

The left hand side is where backup jobs are stored, but we do not have any yet. On the right are three columns. The first contains the source files and folders, and the third contains the destination files and folders. Source and destination folders make a pair and pairs of folders are synced.

At the top of the first column under Compare, is a green plus and Drag & Drop. Drag the source folder, one on the Mac's disk drive for example, from a Finder window and drop it on the first column under Compare. The right hand side of the sync is set up in the same way. Drag the folder to sync with, such as one on the NAS drive, and drop it in the third column under Synchronize.

Click the green plus and you can drag two more folders to Compare and Syncrhonize. So what you do is create a list of folder pairs, with a folder on the left paired with a folder on the right. Each of these pairs of folders will be synced. More folder pairs can be defined - as many as you need.

Click the Compare button and the folders on the left are compared to the folders on the right (and all subfolders too). This produces a list of files to sync.

FreeFileSync - sync folders on the Mac

Before syncing the folder pairs, we need to configure the sync. Click the blue gear icon next to Compare.

FreeFileSync - sync folders on the Mac

Here we can choose how files in the source folder are compared with those in the destination. The simplest is File time and size, and you will use this the most. Select the Filter tab and system folders can be excluded, like the Trash. The ones shown here are set by default.

FreeFileSync - sync folders on the Mac

You can set the time span, which limits the sync to files that are new today, this month and so on. You can set minimum and maximum file sizes to sync, for example if you wanted to ignore extra large video clips, .iso files, virtual machines and so on.

Select the Synchronisation tab and the type of sync can be set. Two way updates each folder in the pair so that they are the same. If there is a new file on the left it is updated on the right, if there is a new one on the right, it is copied to the left and so on. This is useful if you have other Macs syncing with the folder and want to make each Mac the same.

Mirror makes the folder on the right, the destination folder, the same as the source. This is like a simple backup. The Update option copies files from the source to the destination folder, but this won’t necessarily make them the same because it doesn’t delete files in the destination. You can choose how files are deleted, such as permanently vs sending them the to Trash and so on.

FreeFileSync - sync folders on the Mac

I chose Mirror to make a backup to the NAS drive.

Back at the main screen, clicking the Synchronize button starts the sync operation.

FreeFileSync - sync folders on the Mac

Off it goes, syncing the folder pairs between the two disk drives - the Mac’s internal disk and a NAS drive on the Wi-Fi network.

The plan was to back up files in the Documents folder, which was fine, and the Google Drive folder, which hit a snag. The problem was that FreeFileSync creates a temporary file while working and this is updated every second or two. Google Drive was syncing it every time it changed, which made the FreeFileSync slow and generated unnecessary extra network sync traffic between the Mac and Google.

The solution was to quit the Google Drive app while syncing and then run it again afterwards. It is an odd glitch that affected only the Google Drive folder, which is itself synced with Google Drive online, and temporary files elsewhere on the Mac’s disk cause no problems at all.



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