New Mac migration with external drive for SOME files

[Supermacguy]

I am getting a new MBP M4P, upgrade from MBP M1P. My setup is that I have nearly all of my data on an external SSD, including my Photos library, but not my things like email/calendar/contacts. My user folder is on the internal drive. I have a TimeMachine drive also that I let it do a backup of everything, the internal drive and external drive.

I know that when I'm ready to install, I will:
Do a last TM backup, with external data drive connected.
Unplug and shut down old Mac.
Plug external drive and TM drive into new Mac, power on.
I am thinking I will get a Migration Assistant to use my TM backup to install the stuff. Since the external drive will already have everything on it that it is suppposed to, will that be "passed over"? I am hoping it won't want to recopy it and take a full day for a terabyte.

Thoughts? Any roadblocks I'll have?

 

[Bigwaff]

Get Thunderbolt 3 cable, connect both Macs together during initial set up of new MBP, and use Migration Assistant to transfer from your old MBP to new MBP. Way faster than pokey external USB TM drive and no worries about external SSD. After set up complete, attach external SSD.

 

[Brian33]

stuff. Since the external drive will already have everything on it that it is suppposed to, will that be "passed over"? I am hoping it won't want to recopy it and take a full day for a terabyte.

I’m pretty sure Migration Assistant will only migrate files that were on the usual Data volume and will not copy files that were on your external. To be sure, you can elect not to have the external plugged in during the migration. Then plug it in later and everything should be fine.

(I’ve had a very similar setup and migration, but I can’t remember for sure if I had my external plugged in during the migration, or not.)

 

[Fishrrman]

Please forgive me for being a dumb old guy, but some things aren't clear from your original post...

The external drive that has your data on it...
... is it in the form of a tm backup, OR, is it just an external drive that mounts in the finder?

On the NEW MBP, do you want to move ALL your data onto the internal SSD?
or...
Do you want to keep your "current scenario"? (that is, accounts on internal SSD, with some data remaining on the external drive)

I'm going to ASSUME that you want everything on the internal drive.
If it was me, I'd do it this way:
1. when new MBP arrives, connect the backup of your OLD MBP (NOT the backup of the external drive)
2. Run through the setup process, and migrate everything from the OLD MBP.
(now your account is on the new MBP)
Take a few minutes here to "look around" after the migration, make sure your account looks ok, etc. Then...

3. Now you need to move stuff from the external data drive to the internal.
4. You need to do these steps to ensure that there are no permissions conflicts:
a. connect the data drive
b. let its icon mount on the desktop, but DO NOT OPEN the icon yet
c. click ONE TIME on the icon to select it, then bring up the get info box (command-i)
d. at the bottom of get info, click the lock icon and enter the administrative password you're using on the NEW MBP
e. now, put a checkmark into "ignore ownership on this volume" (in sharing and permissions)
f. close get info.
WHY you just did this:
Now, you can copy stuff that was created in your OLD account, to your NEW account on the NEW MBP (the Mac OS normally assumes these to be DIFFERENT accounts).
When you copy (or open) something from the external drive, it will now "come under the ownership" of your NEW MBP/account.

5. Now you can start moving things over. Some things (such as a Photos library) can go directly into your "new" home/pictures, replacing what is there.
Other things will require more thought, such as...
WHERE do you want to put them?
Do you need a new folder created for them?
Etc.
I would get a paper and pencil and keep some handwritten notes during this process to keep track of what's done, etc.

It's not a fast process, requires some attention and forethought, but can be done.
I've done it myself.

Final thought:
If you just want to keep using the external data drive "as it is now", you should be able to do that for the moment. Just connect it and use it.
HOWEVER... you'll still need to take the steps I outlined about permissions above.
I believe that with [the new copy of] Photos, you'll have to tell it to use the external library. To do this, hold down the option key as you launch Photos, then navigate to the external library and choose it.