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need help understanding Time Machine error

In the log output below there is a failure to find a disk matching a UUID but a couple lines later in the log it says the disk mount point is still valid. What does this mean? Are backups working correctly?


2021-10-31 15:18:03 TMPowerState: 2

2021-10-31 15:18:03 Failed to find a disk matching UUID 21E2A2B7-B48B-3EB2-8E9E-5468E48E9AC1

2021-10-31 15:18:19 Mountpoint '/Volumes/G-DRIVE mobile USB-C' is still valid

2021-10-31 15:18:21 Failed to create session for '/System/Volumes/Data/Volumes/G-DRIVE mobile USB-C/Backups.backupdb' with options: 4, error: Error Domain=TMStructureErrorDomain Code=4 "SnapshotStorage - Structure missing" UserInfo={NSUnderlyingError=0x7fea545067c0 {Error Domain=NSPOSIXErrorDomain Code=2 "No such file or directory"}, TMStructureStructureName=SnapshotStorage, NSLocalizedDescription=SnapshotStorage - Structure missing}

2021-10-31 15:18:24 TMPowerState: 2

2021-10-31 15:18:24 Not prioritizing backups with priority errors. lockState=0

2021-10-31 15:18:24 Starting automatic backup

2021-10-31 15:18:25 Mountpoint '/Volumes/G-DRIVE mobile USB-C' is still valid

2021-10-31 15:18:25 Mountpoint '/Volumes/G-DRIVE mobile USB-C' is still valid

MacBook Pro 13″, macOS 12.0

Posted on Oct 31, 2021 3:53 PM

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Posted on Nov 4, 2021 7:32 AM

After dealing with this issue for several days, and running Disk Utility/First Aid on all the drives, and reformatting drives, with no change, I bought a new Samsung T7 2TB SSD for Time Machine backup storage. There have been no issues since installing the new drive 24 hours ago. I suspect macOS Monterey had issues with the G-Technology 1TB G-Drive I was using for Time Machine backup storage. I consider this issue resolved.

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Question marked as Best reply

Nov 4, 2021 7:32 AM in response to jdargie

After dealing with this issue for several days, and running Disk Utility/First Aid on all the drives, and reformatting drives, with no change, I bought a new Samsung T7 2TB SSD for Time Machine backup storage. There have been no issues since installing the new drive 24 hours ago. I suspect macOS Monterey had issues with the G-Technology 1TB G-Drive I was using for Time Machine backup storage. I consider this issue resolved.

Nov 1, 2021 4:57 PM in response to lllaass

Backups are happening just not consistently. About 2 or 3 a day fail. I can click the Time Machine icon in the menu bar and see the status and I can open Time Machine from that icon's menu. I can read write to all drives and my external disks are connected directly to the USB-C ports.


Here is another error I just got: Time Machine could not back up the disk “T7” because a snapshot of the disk could not be created.


"T7" is a new Samsung T7 1gb SSD which can read/write fine and has 884.63gb available with 116.11gb used on disk. It's formatted APFS if that matters (my Time Machine backup disk is a G-Technology G-Drive 1gb HDD formatted Mac OS Extended (Journaled) and has 116.53gb available)


Any suggestions?.

Nov 4, 2021 8:45 AM in response to jdargie

I guess I spoke too soon. No disks were ejected or disconnected and the computer was plugged into power. I don't know how to mark this question as unanswered.


I just received an error:


Time Machine couldn’t complete the backup to “Samsung2tbPSSDT7Media”

One of the disks being backed up may have been ejected or disconnected from the computer.


2021-11-04 07:21:38 Checking destination IO performance at "/Volumes/Samsung2tbPSSDT7Media"

2021-11-04 07:21:39 Failed destination write test with error Error Domain=NSPOSIXErrorDomain Code=60 "Operation timed out". Wrote 17.7 MB in 1 file.


Nov 4, 2021 3:35 PM in response to jdargie

I'm having similar issues. Ever since upgrading to Monterey I can't do a Time Machine backup. I formatted the drive several times. It works for a bit, then the drive just disappears, and it can't mount. I can't repair it via First Aid. The only thing I can do is format it again. If I restart it also disappears right away. I lost all my TM backups and I'm not really keen on rolling back to Big Sur, as I don't want to reinstall applications.

Nov 5, 2021 4:20 AM in response to MersauX

I was using a HDD when all these issues started and switched to an SSD and it didn't seem to fix it. I thought the problem was only on my MacBook Pro 2018 but I've seen it on my Mac Mini M1 also.


2021-11-04 13:44:07  Failed to find a disk matching UUID 260A1CEE-71C0-3A52-B538-6DAC0E9DDE83


2021-11-04 13:44:59  Mountpoint '/Volumes/G-DRIVE mobile USB-C' is still valid


2021-11-04 13:45:01  Failed to create session for '/System/Volumes/Data/Volumes/G-DRIVE mobile USB-C/Backups.backupdb' with options: 4, error: Error Domain=TMStructureErrorDomain Code=4 "SnapshotStorage - Structure missing" UserInfo={NSUnderlyingError=0x146f18fd0 {Error Domain=NSPOSIXErrorDomain Code=2 "No such file or directory"}, TMStructureStructureName=SnapshotStorage, NSLocalizedDescription=SnapshotStorage - Structure missing}

Nov 6, 2021 4:05 AM in response to jdargie

What seems to have solved it for me is using a different cable and port. I initially used a USB 2 port and cable (on my hub), now I switched to a USB C one and port on the hub (for some reason when I plug it into my Macbook it doesn't work at all), and it seems to have fixed it. Time Machine has been working for two days now, I rebooted several times to see if it will get corrupted, it didn't. Hopefully it stays this way.

need help understanding Time Machine error

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