Sierra and Time Machine

When backing up for the first time with OS Sierra, The Time Machine (TM) will require enormous storage on the backup drive. The whole content of the computer will need to be backed up afresh (it won't do a piggy back 'top-up' on the old backup by the previous OS).

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This is how I solved the problem (I am now on OS 10.12.1 Sierra):

1) Stop back-up that is stuck on “Preparing to back-up”. If the preparation and the backup don't start in under a minute, TM is asking for more storage, I reckon.

2) Check storage available:

2a) On top right of the screen:

Time machine preferences > On bottom right, Preferences > Check “Estimated size of full backup: - -” You will need that much space on the hard-drive to do the first back up with the new OS Sierra.

2b) Alternatively, you may find out how much data has been stored on the Mac (the whole of it will need to be backed up!).

Top left of the screen:

Click on the Apple icon on > About this Mac > On top of the new window choose Storage. You will need that much storage (perhaps much more for future top-ups) on the Time Machine hard-drive for the first backup.

2c) Right click on the TM hard-drive on the screen, choose “Get Info” and check whether there is enough storage avaiable for the backup.

You will find that there isn't. That's why the TM can't "prepare".

3) If you now need to backup:

This is now possible only if you have a choice of another place to store (backup), like a larger partition of the same hard-drive or another hard drive.

You will need to choose one of the above:

3a) On top of the screen click on the TM icon > Open Time Machine Preferences. > Select Disk from one of the above two choices (larger partition of the same hard-drive or another hard-drive connected to the Mac) that has enough storage (and more) for the entire data on the computer.

I chose the other partition on the hard-drive. (I didn't need to re-format.) One partition I was using for TM and the other for “drag-and-drop” manual backup of certain files; I clicked on the other larger partition, which had plenty of space.

3b) Choose the back-up to be done on the new drive replacing the old one.

4) Now back up as usual.

Best of luck.

When backing up for the first time with OS Sierra, The Time Machine (TM) will require enormous storage on the backup drive. The whole content of the computer will need to be backed up afresh (it won't do a piggy back 'top-up' on the old backup by the previous OS).

This is how I solved the problem (I am now on Sierra 10.12.1):

1) Stop back-up that is stuck on “Preparing to back-up”. If the preparation and the backup don't start in under a minute, TM is asking for more storage.

2) Check storage available:

2a) On top right of the screen:

Time machine preferences > On bottom right, Preferences > Check “Estimated size of full backup: - -” You will need that much space on the hard-drive to do the first back up with the new OS Sierra.

2b) Alternatively, you may find out how much data has been stored on the Mac (the whole of it will need to be backed up!).

Top left of the screen:

Click on the Apple icon on > About this Mac > On top of the new window choose Storage. You will need that much storage (perhaps much more for future top-ups) on the Time Machine hard-drive for the first backup.

2c) Right click on the TM hard-drive on the screen, choose “Get Info” and check whether there is enough storage avaiable for the backup.

You will find that there isn't.

3) If you now need to backup:

This is now possible only if you have a choice of another place to store (backup), like a larger partition of the same hard-drive or another hard drive.

You will need to choose one of the above:

3a) On top of the screen click on the TM icon > Open Time Machine Preferences. > Select Disk: one of the above two choices (larger partition of the same hard-drive or another hard-drive connected to the Mac) that has enough storage (and more) for the entire data on the computer.

I chose the other partition on the hard-drive. (I didn't need to re-format.) One partition I was using for TM and the other for “drag-and-drop” manual backup of certain files; I chose the latter, which had plenty of space.

3b) Choose the back-up to be done on the new drive replacing the old one.

4) Now back up as usual. It could take several hours to finish backing up.

Best of luck.

My TM backups were stuck "preparing" or taking a full day since the Sierra update, I disabled the app firewall and the packet filter (pf firewall using Muris Lite) and removed an already disabled antivirus (Avast), none of which fixed the issue. Using the steps provided by user Entropee combined with turning off Fire Vault in System Preferences > Security & Privacy solved the issue, TM now backs up in minutes as it did under El Capitan. Fire Vault seems to be the problem using TM in Sierra on my MBP.

Disregard my previous post, File Vault was not a factor, the instructions post by Entropee work, although I was able to leave the firewall on.

I too have been having problems with Time Machine ever since I upgraded to Sierra.

I get past "Preparing Backup" in the back almost completely finishes before I get an error saying "Backup Failed, Time Machine couldn't back up to..."

I was on the phone to say Apple support, they got me to run disk utility, which took for ever and came up with disc errors. Their suggestion was to reformat my Time Machine backup, and they said that there were no known issues with Time Machine and Sierra.

To me, it seemed too much of a coincidence that the morning I upgraded to Sierra was the morning Time Machine stopped working, so I plugged my Time Machine backup into my laptop, which is still running El Capitan, ran disk utility - no errors!

So my advice is be careful, definitely do not delete your Time Machine backup.

I have purchased a new USB hard drive and am backing up successfully from Sierra, but hopefully Apple will release a fix soon so that I can go back to my old Time Machine backup which has the last two years worth of my files!

I upgraded to Sierra and the backup to my Time Capsule was stuck in preparing disk mode and there was a lot of talk on the Sophos Anti Virus site with the same problem, I ran the disk utility which returned numerous errors. I erased and formatted the drive and ran a new backup from scratch. It works fine now except I must first turn off the AV software then initiate a manual backup and after it's complete turn the AV software back on again. Are you running any kind of AV software on your machine?

Well, after having followed entropee's fix and getting my TM to start backing up again, it's suddenly gone back to square one after operating fine for several says, now it's stuck preparing backup. Not sure what caused the change. I had to restart my iMac for other reasons, and afterwards TM stopped backing up. Then I installed Sierra 10.12.1, hoping maybe it might help, but no go.

I had uninstalled Sophos before the fix.

Now I'm wondering if it might be an issue with my ext HD needing to upgrade firmware or software. It's a Lacie Quadra D2, and they do have some info on their site.

http://knowledge.lacie.com/articles/en_US/FAQ/007772en?language=en_US&key=ka03A0 00000tzaWQAQ&kb=n&wwwlocale=en-ca

I have the exact problem, my backup stalls at 160 GB, unfortunately running Mail did not help, can you give me the tmutil script please?

Thanks

PS I am not using any antivirus software at all.

I'm having the same problem where my T.M. stalls after starting to back-up. For some reason, whenever I turn wifi off on my iMac, the backup completes successfully and promptly. If I keep wifi turned off until the next automatic backup, it also completes promptly without any hiccups.

Not sure where's the link but in my case, wifi seems to interfere with my T.M. backup.

I am using a firewire external hard drive directly connected to my iMac.

Before Sierra upgrade, no issues whatsoever of T.M. backups to the same drive.

Hope that Apple is reading this blog and will find a solution to our issues.

Do you use Sophos?

I was using Sophos but I uninstalled it, which did not change T.M. behavior after that.

Uninstalled it properly?

I used the "uninstall Sophos" that came with the program. So I guess it was uninstalled properly.

Do you know a (simple) way to check?

Thanks.

Run an Etrecheck report, post the results here.