Mac – time machine runs very slowly, then stops

backupdisk-utilityexternal-diskhigh sierratime-machine

I've been using Time Machine with my MacBook Pro without issues for some time, however, I’m now having a problem that I haven’t had before: when connecting the external hard drive on which backups are stored, the “Preparing Backup” stage takes an inordinately long time, and when the actual backup starts, it proceeds really slowly (a couple of MB every minute or so) and then it completely stops. I don’t get an error code. This has happened with both Time Machine backup external hard disks that I use.

Could this problem be related to the fact that I’m using two external hard disks for Time Machine backups? I’ve only run backups on two hdd once before.

I’ve run First Aid on one of the external drives but Disk Utility returned an error unmounting the disk. I then ran First Aid on the Macintosh internal ssd drive but Disk Utility returned error: snap_metadata_val objet (oid ox75d3F): invalid externalref_tree_oid (0x0). Snapshot metadata tree is invalid. The volume /dev/rdisk1s1 could not be verified completely.

Any thoughts why this might be happening and how to resolve the issue? I’m running High Sierra on a early 2015 MacBook Pro (upgraded from Yosemite). The two external hdds are formatted as HFS+. I've also swapped usb cables to make sure it's not a faulty cable causing the issue, but the same thing happens.

Best Answer

I've just dealt with a similar issue, and hope I can help someone. I did a completely clean install of High Sierra, then Time Machine stopped working after four days.

Your error message indicates that this is a problem with the drive you're backing up, or perhaps Time Machine's index of it.

Here are the steps to take:

Check your local snapshots, and delete anything fishy - see the empty one from the day that TM stopped working:

You would do this: sudo tmutil deletelocalsnapshots 2018-09-27-003128

Try using disk utility to repair all the volumes and drives again. If it's an APFS drive you're backing up, check all of the volumes, as well as the container volume and the disk. You can try deleting all the local snapshots too, and again try repairing the volumes and disks.
If that doesn't work, I would turn disable Time Machine - go into System Preferences and uncheck automatic backups. Unmount (restart if you have to) the drive with the most recent full backup on it - we don't want to touch that. Then, remove it by clicking "Select Disk" and "Remove Disk." Try a backup then, with just the one drive. If that doesn't work, try repairing that drive again in Disk Utility.
The next thing to try would be to remove the drive that's still associated, rename it "Time Machine Backups," and then add it back. You shouldn't lose the backups that are already there.
If all else fails, I would start over - reformat this drive in Disk Utility, but not as HFS+ Journaled - that was a mistake I made numerous times. We want Time Machine to format the drive. That should at least get you going again...

My problem was that it mysteriously wouldn't copy files.

For a week, no matter what I did, the same thing would happen - Time Machine would start, go very slowly, and then stop and give me this message:

It wouldn't complete an initial backup even. I had reformatted over and over (as HFS+ Journaled), deleted local snapshots, tried repairing the backup drive and the system drive.

The infuriating fix to my problem was simply to remove my encrypted APFS volume. fsck/First Aid kept returning a problem with the container and system volumes - "mount apfs exit status 73" and "System check exit code is 78." All that was happening was that it couldn't mount the encrypted volume. After I deleted that, I was finally able to fix Time Machine.

I still had trouble though, even after zeroing out the first 300MB of the backup drive to totally nuke the partition map and EFI. Eventually I formatted it as exFAT, let Time Machine format it, which it failed to do:

And then I went back to Disk Utility and formatted it as HFS+ Journaled Case Sensitive. That's when it started working.

Modes and ownership

Ideally, use chmod(1) and chown(8) to have the mode and ownership, of the copy of the disk image, consistent with how Mountain Lion normally creates a local disk image for Time Machine.

Example

GPES3E-gjp4-1:~ gjp22$ sudo ls -al /Volumes/tall/com.apple.backupd/GPES3E-gjp4-1.sparsebundle/
Password:
total 16672
drwx------@ 3 root   staff     10  7 Jun 19:07 .
drwxr-xr-x  8 gjp22  staff     10  6 Jun 18:57 ..
-rw-r--r--  1 root   staff    500  7 Jun 18:03 Info.bckup
-rw-r--r--  1 root   staff    500  7 Jun 18:03 Info.plist
drwx------  2 root   staff  78855  7 Jun 19:07 bands
-rw-r--r--  1 root   staff    444  7 Jun 18:02 com.apple.TimeMachine.MachineID.bckup
-rw-r--r--  1 root   staff    444  7 Jun 18:02 com.apple.TimeMachine.MachineID.plist
-rw-r--r--  1 root   staff   1473  6 Jun 21:28 com.apple.TimeMachine.Results.plist
-rw-r--r--  1 root   staff  10698  6 Jun 22:24 com.apple.TimeMachine.SnapshotHistory.plist
-rwx------  1 root   staff      0 19 Mar 19:36 token

– and for each band, you should have:

-rw-------  1 root  staff

Attaching the copy of the disk image

With Terminal, for the example above:

sudo hdiutil attach -readonly /Volumes/tall/com.apple.backupd/GPES3E-gjp4-1.sparsebundle/

If you use Terminal from within Recovery OS: you'll probably not need the sudo prefix to the command.

Additional detail

… whether I can still restore …

You require:

a copy of a Time Machine destination, a copy that will be good for restoration
not an additional Time Machine destination.

Assumption

You wish the copy to be usable, for restoration only, in the event of loss or failure of the Time Capsule.

If the disk is attached from a local image where modes and ownership vary from the norm for a local image:

OS X or Recovery OS might use that disk without difficulty; I can't be certain.

Thoughts

If you're preparing for the possibility of loss or failure of a Time Capsule – and restoration from a copy of what was there – then think a step further, to backing up without the original Time Capsule. (If you wish the copy to be writeable by Time Machine, that could be a separate question.)

All things considered

It's probably quicker and simpler to use the external hard disk, or a part, as a Time Machine destination.

Mac – Does Time Machine take 2 backups or 1 (on 2 external drives)

They are two separate backups. Time Machine will back up to whichever drive is currently connected.

I make use of this to alternate two Macs in my household between two Time Machine disks. Each drive contains a complete copy of each Mac as of the last time it was connected, as well as all past snapshots made to that drive that haven't been deleted to make space. Either one is thus useful on its own for restore purposes, even if the other is destroyed or corrupt.

If you connect two drives simultaneously, the same result occurs (each drive is a complete backup); Time Machine will alternate backing up to each.