Time Machine error: The backup disk image xxx.sparsebundle could not be accessed (error 16)

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Level 1

27 points

Time Machine error: The backup disk image xxx.sparsebundle could not be accessed (error 16)

I'm having issues with Time Machine Backups to a NAS (WD MyCloud EX2 Ultra). The Mac runs macOS 12.2, but I had similar problems with Big Sur.

The initial backup was completed successfully, and TM worked fine for a couple of cycles until it started returning an error:

Restarting the Mac does not solve the problem, but restarting the NAS, the router, or even simply disconnecting the NAS from the router for a few seconds and connecting back allows TM backups to resume.

I believe I’ve been able to narrow down the source of the issue. It turns out there is an smb process (“smbd -D”) that continues to run on the NAS and use the sparsebundle even after Time Machine completes the backup (it’s shown as “R<” in "top"). When Time Machine tries to start the next backup session, it finds that the sparsebundle cannot be accessed, because the smb process from the previous backup session is still accessing it.

After killing the process, Time Machine backups resume for a few cycles, until it happens all over again.

I believe that the issue is somehow unique to that specific Mac (a MacBook Pro). I configured another Mac (a MacBook Air) to back up to the same NAS, the same share, and it works with no issues. The most obvious difference between the two Macs is that the sparsebundle for the Pro is very large (around 2TB; there are 1.5TB of data on the computer). The Air has only about 300GB of data on the disk, and its sparsebundle is much much smaller.

I would appreciate any suggestions on how to resolve this issue.

Posted on Feb 11, 2022 10:29 PM

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Answer 1

zornie Author

Level 1

27 points

Feb 21, 2022 12:57 PM in response to Geoff Fleck

Btw, my Mac had two user accounts under the same Apple ID: one for work and one for home. The home account had large Photos and Music libraries (over 500GB each). I have moved the data from the home account to an external USB drive, and deleted the home account completely from the computer. There are now only about 200GB of data stored on the Mac and only one user account. I have also turned off FileVault. Next, I have re-formatted the MyCloud NAS and performed a full factory reset on it. I'm now staring a new TM backup to the NAS to see if the problem goes away. If it does, I'll try to bring the data back one chunk at a time.

Since TM on the second Mac works fine with the NAS, I'm just trying to rule out that there is something in the data stored on the problematic Mac, the size of the stored data, or something else in the settings in the home account that cause the issue.

I know it's pretty extreme, but I've already spent 3 months trying every other possible solution. Luckily, I have a couple of external USB drives with additional TM backups, which allow me to go through this process.

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Answer 2

Feb 20, 2022 2:39 PM in response to zornie

I would ensure that your WD NAS is fully up-to-date and then contact WD for support. Consider changing to a different NAS product. I would personally recommend a Synology solution. I cannot recommend QNAP due to the myriad of security problems that continue to go unfixed.

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Answer 3

lllaass

Level 10

210,513 points

Feb 21, 2022 6:06 AM in response to zornie

Other users have reported similar problem with WD MyCloud NASs after upgrading to Monterey. I have not seen a good solution except to start a new backup

Can you access the Time Machine by Entering the ™? I am trying see if the existing backup works.

If it works can you create a new share on the NAS and start a new backup?

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Answer 4

Feb 27, 2022 10:01 AM in response to zornie

I tried rebooting the NAS. It's been @week now and since then the backup is running fine. I did make sure that it was the most up to date version of the Cloud OS running on the NAS. Sorry but I can't explain why now it is running without error. I'll update if it starts to act up again.

BTW personal opinion on WD support. They have not been very helpful through this. In spite of providing detailed troubleshooting notes and screen shots they don't seem to read or really study the information provided. They have consistently just provided links to their support articles with instructions on how to do something. For the most part it wasn't helpful and/or didn't answer the question. There was no back and forth troubleshooting dialog.

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Answer 5

Feb 21, 2022 8:52 AM in response to zornie

I have been experiencing the same issue with my WD MyCloud EX2 Ultra since I bought my mew MacBook Pro (M1) just before Christmas. My previous MacBook Pro (Intel) has always worked with TimeMachine & the NAS without issue.

I tried rebooting the NAS and it is working again. However it has as you mentioned been up & down. Working for a few days and then erroring out. The NAS reboot fixes it. This is a temporary work around.

The solution it seems to me is for WD to patch My Cloud OS 5 they pushed everyone onto.

It does seem related to MacBook Pro with M1 silicon.

Both my old and new MacBooks are running the same version of MAC OS Maverick. So that doesn't seems to be the root cause unless Apple changed the Time Machine code for the M1 chips.

I have gone back & forth with WD support on the issue. Their support response has not helped much. A lack of wanting to really dig into the issue. I am going to submit this new information you provided, Thanks for the research btw, and see if it gets them to really look into it and work on a solution.

I did find on the WD site in a article they referred me to that Maverick is not listed as an Apple MAC OS version which is supported by My Cloud OS 5.

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Answer 6

Law Dog

Level 1

13 points

Apr 7, 2022 8:09 AM in response to Geoff Fleck

It has nothing to do with the type of NAS, Synology is having the same problem. This is pretty tiring . . . and I am getting my fill of TimeMachine and its backups.

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Answer 7

zornie Author

Level 1

27 points

Feb 21, 2022 12:23 PM in response to Geoff Fleck

I have an intel-based Mac. I've only used the NAS with Big Sur and Monterey, and the same problem is present under both.

Thank you for submitting the information. I'm also trying to follow up with them, but for now all troubleshooting steps they've suggested are pretty basic and do not resolve the problem.

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