Mac – Time Machine partition won’t mount

disk-utilityhigh sierrapartitiontime-machine

I have an external drive with two partitions, the first of which I use for Time Machine backups. The other day I got a message telling me that my drive had been unplugged without being ejected first (not true). Today when I plugged it in, the Time Machine partition did not mount but the second partition did.

When I try mounting the partition in Terminal I get: Volume on disk2s2 timed out waiting to mount

I tried $ diskutil repairDisk disk2 and got:

Started partition map repair on disk2
Checking prerequisites
Checking the partition list
Adjusting partition map to fit whole disk as required
Checking for an EFI system partition
Checking the EFI system partition's size
Checking the EFI system partition's file system
Checking the EFI system partition's folder content
Problems were encountered during repair of the partition map
Error: -69854: A disk with a mount point is required

I tried $ diskutil repairVolume disk2s2 and got:

Started file system repair on disk2s2 Backup
Repairing file system
Volume is already unmounted
Performing fsck_hfs -fy -x /dev/rdisk2s2
File system check exit code is 8
Restoring the original state found as unmounted
Error: -69845: File system verify or repair failed
Underlying error: 8: Exec format error

I did $ ps aux | grep fsck and got:

root 642 22.8 12.6 6396120 2107688 ?? U 3:27PM 15:48.20 /System/Library/Filesystems/hfs.fs/Contents/Resources/./fsck_hfs -y /dev/disk2s2

According to another thread here, this means that fsck has "hijacked" the partition, but I don't know what that means.

I don't know what to do at this point. My big concern is not losing my Time Machine backups.

Best Answer

Okay, I figured out what was going on: When macOS detects a drive being unplugged without being ejected (which I don't think happened but I did get a message saying it had), the next time you plug the drive in fsck is going to go to work automatically, to check out the drive and attempt to repair it if need be. Unless you go looking, you'll get no indication that this is what's happening other than that the drive (or a partition on it) won't mount. This super helpful comment was key to my understanding what's going on: https://superuser.com/a/1013435/955941. After about 10 hours, fsck finished and the partition mounted correctly.

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