Using WD Passport with two Mac OS Systems

OK, I used a 6-7 year old USB WD Passport drive which was formatted in Mac OS Extended (Journaled).

I connected the drive to my Big Sur laptop and set it up as a destination for Time Machine backups. With no prompting, Time Machine automatically configured the WD Drive in APFS (Case Sensitive) and then backed up the contents of my Mac. About 150 GB was backed up in about 2 hours. Not bad.

Then, I ejected the drive and connected it to my wife's Big Sur iMac and went through the motions of setting up the WD Drive for backups. The following message appeared:

I chose the "Start New Backup" option. As soon as I did this, another hard drive icon named "Backups of (my wife's name) iMac appear on the Mac desktop along with the original drive named WD 500 GB.

The iMac backed up to "Backups of (my wife's name) iMac.

When the backup was done, I ejected the drive and connected it back to my laptop. When I did this, two hard drive icons appeared on the my laptop's desktop.......WD 500 GB and Backups of (my wife's name) iMac.

Time Machine backed up to the correct WD 500 GB drive.

So, you might be OK if you don't want to set up two separate partitions on the WD drive. But.....things would be much easier, with far fewer chances of errors.......if you simply used a separate hard drive for each of your Macs.

Can I use the WD Passport to back up multiple laptops?

Yes, but you will need to set up two separate partitions on the WD Drive, one for the Big Sur Mac and the other for the Mac running High Sierra.

For example, say the WD Drive has a capacity of 2 TB. You would set up one partition of 1 TB and the other also as 1 TB.

The reason......Apple changed the format of the internal disk on Macs that are running Big Sur to a new type of format called APFS. So, the Big Sur Mac backs up to a hard drive formatted as APFS automatically on the first backup to match up the format of the Mac's hard drive with the backup drive.

Older Macs used a format called Mac OS Extended (Journaled), also known as HFS+, so Time Machine backups on older Macs were automatically formatted correctly for Macs at the time.

IF......you had already been backing up your High Sierra Mac to the WD Drive......then......Time Machine on the Big Sur Mac would have likely gone ahead and set up the Big Sur backups using the older Mac or HFS+ format.

Not recommended though, since the Big Sur backups would be stored on a hard drive that is formatted differently than the internal hard drive on the Big Sur Mac. That's bound to result in a conflict at some point with future updates to Big Sur.

If I were gong to do this, I would set up two separate partitions on the WD drive and format both the same way in Mac OS Extended (Journaled) or HFS+. The High Sierra Mac will back up automatically to the partition that you choose, and the Big Sur Mac will automatically reformat the other partition as part of the initial back up process. You don't really have to do anything.....let Big Sur / Time Machine set up the backups automatically.

Any concerns with using this approach?

If you are thinking of updating the High Sierra Mac to Big Sur, you would want to be sure to have a current back up of the High Sierra Mac on a another separate hard drive handy.......just in case things don't go smoothly with the Big Sur update.

Once you have both Big Sur Macs backing up reliably to the WD Drive, then you may want to go ahead and erase the old High Sierra backups on the old hard drive, unless you are in the habit of going back weeks, months, etc to pick up an old file. Few of us ever need that capability.

Just trying to reduce complexity of multiple partitions as I am not that familiar with setting up the WD Passport that way.

I am not sure but the way Time Machine uses a local disk might still requires the use of partitions.

When backing up to a local drive.. Time Machine will tend to use the whole disk.. Bob may want to comment but on previous versions of Mac OS i would not recommend using the same partition or unpartitioned disk on multiple computers.

Disks are cheap. Buy another disk for the other computer. In the long run swapping hard disks around is a good way to break the USB port. For another the WD passport is slow. Test it on big sur computer and see but APFS is optimised for SSD not spinning rust. You might find it is abysmally slow.

Just trying to reduce complexity of multiple partitions as I am not that familiar with setting up the WD Passport that way.

LaPastenague may have a very good point. As I mentioned previously, I would set up two partitions on the WD drive if I was going to try to swap the drive back and forth from one Mac to the other....(not a great idea in my opinion).....whether they were using the same operating system or not.

Much better to use a separate hard drive for each Mac, then you don't have to worry about unplugging and replugging the drive, which will stress the USB ports on both Macs as well as the USB connector on the hard drive.

So, to reduce complexity, the simplest solution would be to use a separate drive for each Mac. Funny how the simplest solutions always seem to produce the most reliable results.

It may take until tomorrow to know the results, but I'll try to set up a spare WD drive here as a single APFS device, make a Time Machine backup of one Big Sur Mac and then try to switch the drive over to another Big Sur Mac to see what happens when I try to back up that other Mac.

At minimum, I would expect to see messages to the effect that backups from another Mac have been detected with some options on how to proceed.

Will post the results when I have completed this "test".

Ended up w/ the same 'duplicate' drives showing in Finder which makes me nervous as I never know when something like this is going to come unwound and randomly stop working.

That is a legitimate concern, since complexity increases the chances of an error occurring during a backup. It simply is not a good idea to be swapping the same hard drive back and forth from one Mac to the other. USB ports and connectors were not designed for this type of use as well.

As I mentioned previously, my laptop had about 150 GB of data and the entire back up took about 2 hours on my 7+ year old WD Drive. That is very good performance, even for a new drive, so I'm not sure about the slowness that you have seen. My wife's iMac had about 300 GB of data and that backup took right at 4 hours, so the back up speeds from both Macs were quite good and about the same.

I haven't tried a solid state external drive, so can't comment on performance in that regard.

You are tired of hearing by now, but you really do need to have a separate drive for each Mac if you are looking for best performance, simplicity and good reliability.