Mac to Mac sync

How does one sync from one mac to another if the hard disks are different sizes, using ChronoSync and ChronoAgent?

Which files do you want to sync and why do you think the differently-sized drives are an issue?

Chronosync does not look at disk sizes but at what files it has to copy, and will give an error if it runs out of disk space. It will copy from a large to a small disk provided there is enough space for the files being copied.

From the Chronosync manual page 82 “If ChronoSync returns a disk full error, check your destination for available space. ChronoSync needs enough space to handle all the files plus twice the size of your largest file”.

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I would like to sync everything that is on one disk to another. Can I use an external disk for the smaller one? Can I decide what goes on the internal and what goes n the external?

I think you are either confused about what you want to do or having difficulty expressing it.

Chronosync will copy whatever you tell it to copy, usually a folder and its contents, from one disk to another. Then, each time it runs, it will keep that folder synchronised with the copy on the other disk. New and changed files will be copied to the destination and deleted files will be deleted from the destination. That’s it (apart from some optional clever handling of deleted files).

You obviously can’t sync everything on a large disk to a smaller disk (unless the large disk isn’t full); Chronosync is a damn fine utility, but it’s not that good.

What exactly are you trying to accomplish?

Thank you Jeremy

Ideally I would like to use one Mac at my desk and another to travel and to have all my information up to date on both when I change computers

I have been using Goodsync for many years. It is highly customisable and might suit your needs.
I have several schemes setup for syncing to different Macs and for syncing certain folders.

I’ve heard great things about Syncthing. It’s like Dropbox in terms of ease of use and integration, but it doesn’t involve a 3rd party cloud. It’s your own peer-to-peer sync tool.

Here’s a rather comprehensive review by Leo Laporte

Jeremy’s approach is what I would recommend if you already own Chronosync.

Identify what you wish to sync and then how you sync it becomes easier to identify.

Perhaps best to consider each computer as its own thing with a folder of synced material on it. Rather than two computers with identical drives in them.

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I’ve been using syncthing for a few years now, and it’s great if you don’t want to trust your data or pay for a cloud syncing service like Dropbox or OneDrive. It wasn’t trivial yo set up back then when it was in beta but I believe it’s easier now.

Chronosync will do bidirectional synchronisation, of course. I omitted to mention that.

For what I think you describe, I use Dropbox. It’s seamless and invisible, once set up: it just works. It has the advantage over Chronosync in that it doesn’t have to be expressly run: it’s always on.

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The easiest way is to use iCloud.

If you don’t have good internet, Chronosync can be used to ‘mirror’ folders… but you have to be extremely rigorous about never mixing up which Mac you’re using. It can only be one, then sync, then another, then sync, then another, etc. etc. etc.

I did this for a number of years and it worked fine… but I did mess up once or twice. Luckily, I’m ‘belt and braces’ and had 2 separate backups via Chronosync… plus Time Machine.

Mirroring Macs for apps and the OS is complex and probably a bad idea.

I have dissimilar laptops: 2019 16" Intel 64GB with 8TB SSD and 2021 14" M1 Max 64GB with 4TB SSD. After much research, I found that the M1 can be made to be the target meaning one “drive” at a time can be visible to the Intel over USB-C cable.

Connect the two with USB-C cable
On M1 at Apple menu do "Shut Down
On M1 press and hold power button until “Loading startup options” appears
On M1 click “Options” and then “Continue” Enter password if requested
M1 now in Recovery Mode
On M1 Choose "Utilities > Share Disk, if locked it will need password
On M1 select disk or volume to be shared
On M1 click “Start Sharing”

On Intel open a Finder window and click on Network below Locations in Finder window sidebar
On Intel in that window click on the M1 “drive/volume” to connect as “Guest” or I used admin password
Files can transfer in both directions

To break connection, Click on M1 Apple menu and select restart

Could not successfully reverse the roles of the computers which does not matter as the method above can move files in either direction

That is the new Target Disk Mode on Apple Silicon (here it’s actually now called Disk Sharing and technically relies on SMB). But the original TDM existed long before already and so you can most definitely get it to work on your Intel MBP if you choose. The way to get there is just slightly different. Instructions can be found in this Apple doc.

And in order to get best performance, try using TB4 cables instead of just whatever USB-C you have laying around. They’re better for several other reasons anyway.

I could get the 16" Intel into target disc mode but the 14" M1 Max could not see it. So for my equipment, the procedure I detailed above is my only option other than using my NAS which is slower than a turtle with a limp.

So far I have an Intel MBP. I was dreaming of getting a Silicone Studio but decided my aspirations were not reasonable.
I’m postponing my project

Thanks to all who have chimed in!