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Question: Copy Time Machine or Start New?

Looking to understand if I should copy the existing TM backup files, or start a fresh new backup on the new disk.

I'm replacing the external drive on my iMac that has been used for TM backups with a new and larger unit.


Would appreciate your thoughts on pros and cons of:

A) starting a fresh TM backup on new drive; holding the old drive for a period to ensure prior files not needed

B) copying over the TM backup files from the old disk drive


My TM backup archive is extremely large -- this is a mid-2010 iMac and the TM backups have consumed 995GB of a 1TB partition.


Full Disclosure: I followed Apples method to copy the old TM backup to new drive, and after 15 hours, Finder was in the "preparation" phase and had not started copying any files. I stopped the copy as this got me thinking if I really needed to retain this much "old archive". In the seven years I've used the Mac, I've never had reason to go back and grab a file from TM backup.


Comments greatly appreciated.

iMac, macOS Sierra (10.12.6)

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Nov 11, 2017 7:47 AM in response to weskat In response to weskat

Method A)


I’ve just copied my existing Time Machine Backup to a new drive. It took about 25 hours (over USB 3) but it did the job okay. It took 12 hours or so just to work out what it was about to copy across, then a similar amount of time to copy across about 2.5 million items. The file was similar in size to yours because my backup also goes back to 2010 or thereabouts.


My original iMac had a 750GB internal. My new iMac has 3TB. My Backup HDD is 1TB RAID 1 device. I’ve just transferred to a 16TB configured as 8TB RAID 1 (it has two 8TB physical drives that are now mirrored. I have further partitioned each volume as two 4TB volumes, one of which is now my Time Machine backup.


It seems to be working fine right now although I did get an apparently spurious error message at one point. I think that if you had let it carry on, you will have finished backing up by now. I suggest that you reinitialise or wipe the new drive and start the copying process again.


The reason I got a new iMac is because the other one gave up the ghost. My Time Machine backup saved my bacon. I lost nothing.

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Nov 11, 2017 7:47 AM in response to El Deanio In response to El Deanio

Sorry, I meant Method B.


The file size I had was about 840GB. I started the copy process at 7am last Saturday (4th November 2017). It finished sometime early Monday morning. That is, it was finished by the time I went to work at 6:15 am last Monday morning.


But it was worth it.

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Question marked as Helpful

Nov 11, 2017 7:47 AM in response to weskat In response to weskat

Method A)


I’ve just copied my existing Time Machine Backup to a new drive. It took about 25 hours (over USB 3) but it did the job okay. It took 12 hours or so just to work out what it was about to copy across, then a similar amount of time to copy across about 2.5 million items. The file was similar in size to yours because my backup also goes back to 2010 or thereabouts.


My original iMac had a 750GB internal. My new iMac has 3TB. My Backup HDD is 1TB RAID 1 device. I’ve just transferred to a 16TB configured as 8TB RAID 1 (it has two 8TB physical drives that are now mirrored. I have further partitioned each volume as two 4TB volumes, one of which is now my Time Machine backup.


It seems to be working fine right now although I did get an apparently spurious error message at one point. I think that if you had let it carry on, you will have finished backing up by now. I suggest that you reinitialise or wipe the new drive and start the copying process again.


The reason I got a new iMac is because the other one gave up the ghost. My Time Machine backup saved my bacon. I lost nothing.

Nov 11, 2017 7:47 AM

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Nov 11, 2017 7:47 AM in response to El Deanio In response to El Deanio

Sorry, I meant Method B.


The file size I had was about 840GB. I started the copy process at 7am last Saturday (4th November 2017). It finished sometime early Monday morning. That is, it was finished by the time I went to work at 6:15 am last Monday morning.


But it was worth it.

Nov 11, 2017 7:47 AM

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Nov 11, 2017 7:47 AM in response to El Deanio In response to El Deanio

Hi El Deanio - really good input, thanks. I think you're right, if I'd left it run long enough it would copy all the files to the new drive. After 15 hours it was probably about done with the "preparation" and ready to start copying.


But I'm pondering if I really need to keep all file revisions for all the files since day one. Since TM never notified me it was deleting backups, I believe each version of all files are there, going back to early versions of OSX formats that I would never use.


What would be the downside of starting a fresh TM backup... of course, holding on to the prior TM backup files until I was sure they were not needed?

Nov 11, 2017 7:47 AM

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Question: Copy Time Machine or Start New?