How to inherit multiple backup disks to existing Mac (with previously synch'd file system)?

I do in fact have the drive (and it is a fast SSD), and so what you suggest is a nice idea. The only drawback is that I need to boot to that drive if I want old versions of files, rather than having the convenience of accessing all old versions of my files from my MBAir.

If this is occurring on a regular basis you are using the wrong software. Time Machine is not a proper archive/versioning software. It will wipe out files that no longer exist on the Mac. It will also remove a whole bunch of versions as part of its thinning process. It certainly does not keep all versions.

How often are you digging around for old versions of files? How far back are you going?

Indeed, I did not realize this. I'm not sure I understand though: am I able to access past versions of the same file (albeit not using the TM interface)?

Yes, It is easy to drill down using Finder to extract files from Time Machine backup. Just pick the date you want and go to your user files and check for it.. sometimes you will need to check in a few of the dates as mentioned.. TM thins the backups. Not every variation is present.

I would also comment that booting from SSD after the first time when changes are made to install is very fast over USB3. You can literally boot the machine in a minute.

I'm not sure which "settings" you mean, but the MBPro and MBAir had a virtually identical environment, save for files that are somehow machine-specific - though these would be system files, and I'm really not concerned with those, I just want to be able to access old versions of user files - but from the MBAir now rather than the defunct MBPro.

Lots of things are different. There are various identifiers added to hard disk so each machine cannot directly use the same Time Machine backup. It is not based on computer name. When you inherit a backup major changes are made.. and I don't know what the implications of all of those changes are.. but we have found Time Machine is increasingly fragile.

If you really wish to make the Air identical to the Pro you can do it. Let me explain.

Do use the SSD from the pro and plug it into the Air and boot from it.. if that works well.. very well.. and you can then also access the backups.. clone the Pro drive to the Air having cloned the Air drive somewhere else. I use Carbon Copy Cloner to do this. It is free to download and use for a month without limits.

Test test test. Once you create a clone of the Air .. boot from it .. so you know it works. Once you are happy it works.. clone the SSD of the Pro which is now working on the Air to the Air internal drive.

From now on I would look for proper archive software.. to hold all the versions of your various files that your constantly referencing because I can guarantee you the day will come when Time Machine does this.

I see it annually if not more often.

You will cry a lot when this happens.

LaPastenague is the expert on topics like this, so please wait for his reply. He's in Australia, so it may be awhile due to the time difference.

In the meantime, I'm going to do my best to try to convince you NOT to try to inherit backups, since this is a real mess......even when things are simple and you have a "new" Mac, and have used Setup Assistant or Migration Assistant to set up the new Mac using a backup of the "old" Mac.

If things have been done like this, then the option to "inherit" the old backups or start a "new" backup of the new Mac will automatically appear when you run Time Machine on the new Mac for the first time. I do not know if there is a manual way to tell Time Machine to "inherit" the backups from another Mac. Don't think so, though.

You have a special case, and based on what I know and have tried in the past, it will not be possible to "inherit" the backups.

But, let's wait for the expert on this to respond. I'll keep quiet now and will not post again unless I can add something.

What you are doing is very unusual and I don't have direct experience. Unfortunately experimenting is not really an option here because you will really mess up the older backups doing it.

You can inherit one of the backups I guess.. but I am with Bob on this one.. since the computers were synced but never actually connected via Time Machine at any previous point you are likely to damage to current install or the backup or both.

Tell us why?

Is there something lacking in the Air that you need? Or are you simply trying to make the old backup available on the Air? Or???

If you have important business info in the backup first point is to preserve one of the backups at least. That is crucial. Time Machine backups are a lot more fragile than you might think. You can archive the TC for example to a portable USB drive and keep that. Then erase the TC and start Time Machine backup. That will then be specifically for the Air. What we normally recommend to people is to keep this running for say 6 months and then you can also clear USB drive and start using that as well since you are unlikely to need older files.

I do have a suggestion though. Good bad or otherwise it might be worth a go depending on what you are trying to achieve.

Edit.. or pull the existing disk from the MBP if it is still ok and use a suitable USB holder and plug it directly to the Air and boot from it.. that saves all the following mess.

Create a copy of your MBP boot disk to a decent fast USB drive.. even SSD. It only needs to match the size of the drive in the old MBP. You do this by using setup assistant in recovery. So plug the drive into the MBA and boot it to recovery. You will find Time Machine is available there and you can select the backup of the MBP. And be very careful to select the external drive as the target not your boot drive in the Air. This will take several hours and will recreate the MBP boot drive.

Once that completes attempt to boot the Air from this drive. This may or may not work.. but Mac OS is fairly flexible and it is usually able to locate all the necessary drivers etc. As long as the machines are similar enough my experience is that it normally works. If it is successful this will give you a working boot of what is effectively your old Machine and can use the backups without much problems.. making sure you keep at least one backup as archive that will not be harmed. Now you can do anything you like with this setup.. including copy across the updates to any files since the MBP broke down. That also ensures you have access to the old keychain for example and other settings that the sync software may not manage to copy across. This method has got a lot of people out of trouble.. but for long term use I am not sure it is particularly useful so we go back to why are you trying to do this??

I am out of edit time.. but it strikes me you may not realise you can open the old backup and use files from it in the Air.

The problem with inheriting the backup is that all the settings will be switched to the values for the Air.

On the other hand if you migrate settings to the Air you will discover the Air is now basically become the Pro.

Starting clean Time Machine backup for the Air is really essential if you wish to have usable backups long term.