Question: Can you use one drive for both Time Machine backup and saving a clone of the macOS?
It would be possible to use a single drive for both a clone drive and a Time Machine drive, but as you’ll soon see, this is very complicated to accomplish.
You would first have to use the entire drive as a clone, and then repartition the unused space to use as the Time Machine backup. The reason for this is that when you create a clone, it must create a small partition in a special place on the drive. This partition is also a part of the internal drive that you don’t see, which is technically the Restore partition of the internal drive. If you first partitioned the drive then tried to use one partition for the clone, that Restore partition might not get created properly. Furthermore, if you first divided the drive into two partitions, the chances are that you won’t be able to boot up from that drive at all.
There’s another very good reason to use two separate drives, one for a clone and the other for Time Machine. The clone, being bootable, would allow you to boot up from that drive when your internal drive fails completely. You then update that clone from the Time Machine backup and the most you will have lost is one hour of any changes you made. This allows you to continue using your computer, although it will take a longer time to boot up and log in. But you could instead replace the internal drive with the clone drive to get it to boot up faster (can only be done if the interface of the two drives are the same and if the clone drive can fit in the same space as the internal drive, size in GB does not matter). When you are ready to replace the bad drive, you first clone it from the clone drive, and no further update from the Time Machine would be necessary when you put the new drive in the computer if you had already updated the clone from Time Machine.
Please view the following video on MacMost.com: https://macmost.com/time-machine-versus-cloning.html. It explains the real difference between a clone and Time Machine. What it doesn’t mention is that you cannot boot up from a Time Machine drive, but that you can boot up from a clone drive.
Now, for some people, keeping a clone is irrelevant. This is because you can either get a new computer with the OS already on it that you can simply update from a Time Machine backup, or you can install a new instance of macOS onto the new drive from the Internet using the Restore function by holding down the Command key and the R key together when you start the computer. You then update from the Time Machine backup. However, having a clone drive simply means not having to wait on the Internet to download the OS.
John R Carter, Sr.