Time Machine questions

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Level 1

5 points

Time Machine questions

Hi,

I'm ready to set up TM for my MacBook Air for the first time. I've read Apple's information about it and still have some questions.

First, can I use the Mac while Time Machine is backing up, or should I start the backup only when I won't be using the Mac for a while? How long does a backup typically take?

Next, it's not clear to me whether I can access files on the external drive I'm using with Time Machine. It seems like this is storage that's all-or-none--I can use it to restore files if there's a catastrophic loss of information from the Mac, but I can't (or shouldn't) go there to retrieve one particular file that was removed from my Mac since the previous backup.

How does the backed-up material relate to what I have stored on iCloud, that also appears on my Mac? I have more on iCloud than is on my Mac, because it has stuff from my iPad too; the external drive has space for what is just on the Mac, but not for all that's on iCloud. So this external drive will back up what's physically on the Mac, and not what's on the iPad, even though the iPad files "appear" on the Mac because they're in iCloud. Is that right?

Thanks for any light you can shed on this.

MacBook Air 13″, macOS 12.2

Posted on Mar 7, 2022 9:51 AM

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Answer 1

John Galt

Level 10

146,516 points

Mar 9, 2022 11:10 AM in response to che47

Next, it's not clear to me whether I can access files on the external drive I'm using with Time Machine.

By default Time Machine backs up all mounted drives — with the exception of the Time Machine volume itself, which cannot be backed up (but it can be duplicated, for whatever reason you might want to do that).

It seems like this is storage that's all-or-none--I can use it to restore files if there's a catastrophic loss of information from the Mac,

You can use TM to restore individual files or the entire source volume.

... but I can't (or shouldn't) go there to retrieve one particular file that was removed from my Mac since the previous backup.

You can retrieve any file that TM has not deleted yet. TM deletes old and "expired" backups when it needs the space they require for newer ones.

The salient point to keep in mind is that if you delete a file from your Mac, TM assumes you don't need it any more. That file then becomes a candidate for deletion, but it will defer that deletion as long as it can. It can remain available to restore for months or years, depending on the capacity of the TM backup device.

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Answer 2

che47 Author

Level 1

5 points

Mar 9, 2022 11:18 AM in response to John Galt

Hi, John

Thanks! It's good to know I could retrieve just one item, if need be, and that TM will keep items deleted from the Mac until it needs the space for something new.

As it happens, I'm right now running TM for the first time. About half an hour to go. The amount of stuff it says it has to back up is several hundred gigs less than the Mac says is on it--I'm guessing this is the twilight zone stuff you referred to in our other thread (Mac's own backups, etc.) It will be interesting to see how much space the Mac says it has available once the TM backup is complete.

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Answer 3

che47 Author

Level 1

5 points

Mar 9, 2022 11:22 AM in response to John Galt

Whoops, wait a minute. This is weird. The external drive and the Mac have the same storage capacity, 1 TB. They're both saying nearly 1 TB has been backed up already, but the backup is a bit less than 60% complete. What's going on there? Does the external drive really have only about half the advertised space? What will happen when it reaches 1 TB stored--stop the backup?

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Answer 4

John Galt

Level 10

146,516 points

Mar 9, 2022 11:38 AM in response to che47

Before it starts an incremental backup, TM will estimate how much space it will require. Its estimate is fairly conservative, because it does not want to begin backing up only to tell you it failed. That can happen, but it's rare.

The amounts "Backing up xx of yy GB" are also estimates that can be wildly inaccurate. The only way to tell how much was actually backed up is to examine its log entries after TM finishes. In every case I examined, the amount of data backed up was always less than what it reported was going to be backed up, often a lot less — the reason for its conservative estimate.

All this pertains to incremental backups, which of course you have not yet seen. The initial backup is by far the most time-consuming, but since initial backups occur very infrequently I have a lot less experience observing them or performing any in-depth analysis. Since Apple is constantly changing the way TM works, it's not worth the time and effort spent examining it.

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Answer 5

che47 Author

Level 1

5 points

Mar 9, 2022 11:49 AM in response to John Galt

OK, good to know.

It finished (earlier than estimated) with about 50 GB of space remaining on the external drive and 62 remaining on the Mac (same as before the backup--I still am not able to get the amount of space available to go up, no matter how much I delete--the Mac will soon become nothing more than a storage device itself).

Anyway, can I just eject the external drive? Even though it says the backup is complete, when I try to eject it, a popup says it wasn't ejected because one or more programs may be using it. If I click Force Eject, it warns me the disk or the info on it could be damaged. TM is set for manual backup, so there shouldn't be any program using it. Should I Force Eject it anyway?

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