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As of 1/1/2017, my Time Machine backups are failing with the following message:

Time Machine couldn't complete the backup to "WDMyCloud". An error occurred while copying files. The problem may be temporary. If the problem persists, use Disk Utility to repair your backup disk.

The drive itself is a 3TB Western Digital My Cloud NAS. I can mount it in the Finder and it seems to be okay (in that I can browse it and open files), but it doesn't appear in Disk Utility at all, which doesn't seem right...

I ran the full diagnostics test in WD's utilities (it exposes a page at wdmycloud.local when the drive is powered on) and it reported no problems.

I've tried restarting both the drive and my MacBook Pro, which didn't help.

Is this a fixable problem, or is my drive dying? I'd be surprised if it's the latter, since it's less than three years old, sits untouched next to my router in a well-ventilated area, and again the diagnostics reported no issues.

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Looking for backup errors in the log, what I found was ; backupd[3278]: objc[3278]: __weak variable at 0x7f9227c07600 holds 0x7f9227c00003 instead of 0x7f9227c0e060. This is probably incorrect use of objc_storeWeak() and objc_loadWeak(). Break on objc_weak_error to debug

Searching for these terms, I found this solution, which solved my issue: https://discussions.apple.com/thread/7686484?start=0&tstart=0

theperlarsen Dec 27, 2016 9:40 PM in response to theperlarsen Level 1 Level 1 (4 points) Dec 27, 2016 9:40 PM in response to theperlarsen SOLVED: Turning off iCloud Drive fixed the issue for me.

The weak variable error in the console is misleading. The logging mechanism was changed for macOS Sierra. Use the paste command into a terminal to view time machine errors:

log show --predicate 'subsystem == "com.apple.TimeMachine"' --info --last 4h | grep Error

I saw lines containing starting with:

Error: (-34) SrcErr:NO Copying Copying /Users/myusername/Library/Mobile Documents/ ...

The mobile folder is used by iCloud drive, so I turned that off. That allowed the backup to complete. Hope this helps others that are experiencing this issue. Hopefully the final version of 10.12.3 fixes this.

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    In my case, the following caused the error, and I deleted the folder :: 0 backupd: (TimeMachine) [com.apple.TimeMachine:TMLogError] Error: (-8062) SrcErr:NO Copying /Volumes/com.apple.TimeMachine.localsnapshots/Backups.backupdb/?/2018-11-11-174047/Macintosh HD/Users/*/Library/Containers/com.nektony.App-Cleaner/Data/Library/Application Support/App Cleaner & Uninstal‌ler/auth.cer to /Volumes/TimeMachine 2TB/Backups.backupdb/*/2018-11-11-174048.inProgress/?/Macintosh HD/Users/*/Library/Containers/com.nektony.App-Cleaner/Data/Library/Application Support – goodhyun Nov 11 '18 at 9:24
  • The ~/Library/Containers/com.nektony.App-Cleaner/Data folder was in my error logs too. I uninstalled the app, and removed Library/Containers/com.nektony.App-Cleaner/Data. Then I killed the local Time Machine snapshots, in case they contained any parts that were corrupted too with tmutil listlocalsnapshots / and sudo tmutil deletelocalsnapshots <date part of snapshot>. – Courtney Faulkner Mar 19 at 18:18
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It could be a corrupt file on your Mac, rather than a problem with the external drive. If it is you can open console via launchpad, and search for error messages related to "backup". If there's a line with something about "SrcErr" and "Copying" and a filename, that will point you to the corrupt file. Either delete it, or go into Time Machine settings and exclude this file from your backups.

I just had this problem, and found the suggestion in this forum: https://discussions.apple.com/thread/7734594

linking to this page which appears to be the original source of the info. http://pondini.org/TM/C3.html

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If the myCloud is a network-connected drive, it won't appear in Disk Utility. Only locally connected drives appear there. As per this answer on Apple's forum site, the way to check your hard drive for errors is to connect it directly to your Mac using USB, FireWire or Thunderbolt. Then you can repair or erase it with Disk Utility. If this hard-wire connection is not an option, you may want to consider erasing the old backup and creating a new backup.

  • Yes, it's a NAS – I didn't realize it wouldn't show up in Disk Utility, thanks! Maybe then this is just a Time Machine issue and the disk itself is fine. I'll see if I can find a USB cable while the diagnostic thing is running... – daGUY Jan 7 '17 at 18:38

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