Changing computers

phiman wrote:
I have a full Time Machine Backup Disc…I would like to use it for Time Machine backups on a new computer and save only the last backup from my previous Time Machine runs on my retiring computer. Can I do this???

If the disk is big enough, sort of. Assuming your new Mac is running Snow Leopard, when you do the first backup it will give you this option:
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If you choose "Reuse Backup," Time Machine will do a new, full backup of the new Mac, and "append" it to the backups of the old Mac. Since your TM drive is already full, it will have to delete a lot of old backups to make room. But it will delete the oldest ones first, so as long as the drive is well over 2.2 times the size of the data it's backing-up, there will be enough space.

As new backups are performed, of course, the older ones will be deleted to make room, so sooner or later, all the backups of the old Mac will be deleted.

But if you want to keep that last backup indefinitely, there's no easy way to do that. The simplest way would be to just start fresh on a new drive, and keep the old one "on the shelf" until you're sure you don't need it anymore.

See #B5 in [Time Machine - Troubleshooting|http://web.me.com/pondini/Time_Machine/Troubleshooting.html] (or use the link in *User Tips* at the top of this forum), for details.

I am having trouble getting this to work. I am moving from my old MacBook (mid 2007) to a new MacBook Air 13". I used migration assistant with my Time Machine HD to migrate my home folder (using your website, Pondini, as a guide, and also to sort out the differences between Setup Assistant and Migration Assistant – thanks for that!).

Now I would like to get my Time Machine HD backing up the new MBA, preferably through the Reuse Backup option. I plug the HD into the MBA (iomega 250 GB). I open Time Machine Preferences. I turn Time Machine ON, using the enormous industrial-grade toggle switch. I select the disk, Optimus Prime. I command it to Back Up Now. I expect to the see the window from your screenshot. I do not see it.

Instead, it steps through the first phases of the backup process, "calculating changes", "cleaning up", and then I get this message (I would insert a screenshot but I don't know how to):

"Time Machine could not complete the backup. This backup is too large for the backup disk. The backup requires 92.43 GB but only 63.03 GB are available....". As mentioned, the drive is 250 GB. The entire contents of the MBA drive is 82 GB, so 250 GB should be well beyond the 2.2x requirement. Even still, maybe the issue is just that it I need more space.

However, from what I can tell, it seems that it's not even offering the option to Reuse Backup, and instead is jumping straight to Create New Backup. Firstly, I would expect it to give me the option before "calculating changes" and "cleaning up". Secondly, after it tells me that there is not enough space, and after I cancel the backup, when I go look at the Optimus Prime volume, there are two separate folders within Backups.backupdb: John Doe's MacBook (full of all the backups from the old machine) and John Doe's MacBook Air, which contains one file, 2010-12-28-012033.inProgress.

If it were going to reuse the old backup, I would expect it to put the new backup in the same folder that contains all the old backups, rather than creating a new folder (and maybe change the name of that folder to the name of the new computer). Am I right about this? Or should it create a new folder, even if it's reusing the old backups?

Anyway, all of this leads me to believe that it's skipping over the Reuse Backup option and going directly to Create New Backup. What do you think?

jam27 wrote:
. . .
I expect to the see the window from your screenshot. I do not see it.

We have a few reports of that; it's not clear just why it happens. 😟

Instead, it steps through the first phases of the backup process, "calculating changes", "cleaning up", and then I get this message (I would insert a screenshot but I don't know how to):

Not needed, since you quoted the message, but for future reference, see See the Images section of the [How can I format my post?|http://discussions.apple.com/thread.jspa?threadID=121950] tip in the [User Tips Library|http://discussions.apple.com/forum.jspa?forumID=599] forum.

However, from what I can tell, it seems that it's not even offering the option to Reuse Backup, and instead is jumping straight to Create New Backup.

Yes, and that's why it's not deleting old backups to make room; it won't delete backups for a different Mac.

It's a long shot, and you have to be very careful, but you might be able to get it to work by manually deleting the +*John Doe's MacBook Air+* folder via the Finder, then emptying the trash. Be certain not to move, change, or delete anything else in your backups, as that can corrupt them, often beyond repair.

Then do a "full reset" of Time Machine, per #A4 in [Time Machine - Troubleshooting|http://web.me.com/pondini/Time_Machine/Troubleshooting.html] (or use the link in *User Tips* at the top of this forum); also Repair your backups per #A5 there; and try the backup again.

If it still won't give you the "reuse" prompt, you're probably out of luck; I've not heard of any other way to get it to behave properly. You could manually delete a number of old backups, but not via the Finder; see #12 in [Time Machine - Frequently Asked Questions|http://web.me.com/pondini/Time_Machine/FAQ.html] (or use the link in *User Tips* at the top of this forum). The other downside to that is, you'll have to continue deleting them manually until they're all gone, since Time Machine won't do it for you -- it will only delete old backups from the new Mac.

It might be better to get another drive, and start fresh on it. You can still view and restore from the old ones, via the +*Browse ...+* option, in #17 of the FAQ.

Thanks. I tried all those steps (deleting the +*John Doe's MacBook Air*+ folder — had already tried this a couple times; repairing the disk; and doing a "full reset" by deleting the plist file) and it still doesn't work.

All I really want to do is keep a copy of the latest backup from the old MacBook until I'm satisfied that everything was transferred to the new Air successfully; I don't care about keeping all the older backups. So I could go through the old backups and delete all of them except the latest (using the "Star Wars" procedure that you outline) and then hopefully that gives me enough room start with a fresh new backup of the new Air. If I do this, is it a good idea to start the new set of backups on a separate partition (so that I can later delete the older partition once I'm satisfied that I no longer need it)?

I would shelf the current HD and start anew on a fresh HD as you suggest, but I only have the one HD and I don't care to buy another. Thanks for all your help on this!

jam27 wrote:
Thanks. I tried all those steps (deleting the +*John Doe's MacBook Air*+ folder — had already tried this a couple times; repairing the disk; and doing a "full reset" by deleting the plist file) and it still doesn't work.

Rats. It occasionally does that, and nobody seems to know why, much less how to fix it. 😟

All I really want to do is keep a copy of the latest backup from the old MacBook until I'm satisfied that everything was transferred to the new Air successfully; I don't care about keeping all the older backups. So I could go through the old backups and delete all of them except the latest (using the "Star Wars" procedure that you outline) and then hopefully that gives me enough room start with a fresh new backup of the new Air.

Yes. You can figure out whether there will be room. The last backup from the old Mac will be almost the size of what was on the old Mac; the new one will be almost the size of what's on the new one, but Time Machine will need another 20% of the new one for temporary workspace. So if you transferred everything from the old Mac to the new one, your TM disk needs to be at least 2.2 times the size of the data.

If I do this, is it a good idea to start the new set of backups on a separate partition (so that I can later delete the older partition once I'm satisfied that I no longer need it)?

Yes, but you almost certainly can't do that, at least not without a 3rd-party app. The reason is, partitions must occupy contiguous physical space on the disk. As backups have been added and deleted, files are no doubt scattered over the disk. Even if you delete a lot of old backups, there likely won't be enough contiguous space to make a partition large enough.

The 3rd-party app iPartition can do that, but they strongly recommend backing-up the data before using it, in case something goes wrong.

I would shelf the current HD and start anew on a fresh HD as you suggest, but I only have the one HD and I don't care to buy another.

I understand, but you'll have to spend some $$ on iPartition or the like and risk losing the backups if there's a problem. And it will take a while to delete the old backups, too.

HDs are relatively inexpensive these days. Your best bet may be to get a new drive and start fresh on it. Once you're sure you don't need the old backups, erase them and start doing "secondary" backups. That may sound like overkill, but all hardware fails, sooner or later, and no backup app is perfect. It's rare, but there are several posts here where a backup drive failed while doing a full restore, and everything was lost.

See #27 in [Time Machine - Frequently Asked Questions|http://web.me.com/pondini/Time_Machine/FAQ.html] (or use the link in *User Tips* at the top of this forum), for some suggestions.

Thanks for all your help on this!

You're quite welcome -- sorry we couldn't persuade TM to act right.