diskmanagementd writing to external disk which is not yet mounted

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claudio1961 Author

Level 1

8 points

diskmanagementd writing to external disk which is not yet mounted

Hi,

I connected the external disk on which I usually backup to my laptop. I noticed that some disk activity started right away. But hours later the still continues, and the drive did not yet show up in finder.

Looking at the activity monitor I first noticed that something is writing to the drive with about 35-45 MByte/second.

I then looked with ps -ef | grep fsck to see if some repair was going on, but no fsck is running.

diskutil list shows, that the mount has not yet happened:

/dev/disk4 (external, physical):

#: TYPE NAME SIZE IDENTIFIER

0: *2.0 TB disk4

disk4 is visible but no partition, that would normally show up as disk4s1 etc.

Finally I found the hint to use the command sudo fs_usage -f filesys and when I do I see it write in fast succession entries like

19:44:47.846486 WrData[S] D=0x7c660e00 B=0x20000 /dev/disk4 /dev/rdisk4 0.003661 W diskmanagementd.2878

19:44:47.846489 write F=3 B=0x20000 0.003671 diskmanagementd.2878

19:44:47.850058 WrData[S] D=0x7c660f00 B=0x20000 /dev/disk4 /dev/rdisk4 0.003560 W diskmanagementd.2878

19:44:47.850062 write F=3 B=0x20000 0.003569 diskmanagementd.2878

19:44:47.853341 WrData[S] D=0x7c661000 B=0x20000 /dev/disk4 /dev/rdisk4 0.003251 W diskmanagementd.2878

19:44:47.853343 write F=3 B=0x20000 0.003261 diskmanagementd.2878

19:44:47.856568 WrData[S] D=0x7c661100 B=0x20000 /dev/disk4 /dev/rdisk4 0.003215 W diskmanagementd.2878

19:44:47.856569 write F=3 B=0x20000 0.003221 diskmanagementd.2878

hinting that diskmanagementd is the culprit of all this writes. What I do not know though is how to deal with this. Shall I just let it continue run, will it end at some time?

Shall I stop it, but if how to do it in a way that is safe, because I do not want to corrupt the disk. I am just in need to retrieve stuff from my backup and thus I don't want to risk to damage it.

If anybody knows more about what could go on, please tell me.

Thanks.

MacBook Pro 15″, macOS 10.15

Posted on May 31, 2020 10:48 AM

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Answer 1

Kappy

Level 10

362,007 points

May 31, 2020 11:05 AM in response to claudio1961

What is most likely happening is that the OS is trying to mount the drive, repeatedly. Just disconnect the drive. If that doesn't return things to normal, then reboot the computer.

As for the external drive, it's possible that it just needs formatting. It's also possible the drive is damaged or failed.

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Answer 2

Kappy

Level 10

362,007 points

May 31, 2020 11:26 AM in response to claudio1961

It certainly would seem so. The OS performs a number of operations when mounting a drive. I don't know what those operations are, specifically, so I'm implying that is why you see the write activity. You will note that it's the same attempt each time. I don't know how many bytes it may write in those time frames but could be quite a bit.

Regardless, there is a problem with the drive, so I would remove it. The continuous activity should cease. Is there something on the drive you fear losing? If so, then try a shutdown. Even a forced shutdown should not cause more damage than may already exist. If you shutdown the computer, then remove the drive, you won't have any problem with the data on the drive beyond what may already exist.

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Answer 3

claudio1961 Author

Level 1

8 points

May 31, 2020 11:17 AM in response to Kappy

Hi,

thanks for your answer. And you think that trying to mount over and over again is consistent with all this writing that occurs? If it would just be reading I would be more confident in detaching the drive. But reading does almost not happen (mostly 0 bytes sometimes a few ten KBytes/second) while writing is constantly around 35-45 MByte/second.

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Answer 4

claudio1961 Author

Level 1

8 points

Jun 5, 2020 10:40 AM in response to claudio1961

Hi,

for the posterity a first update. Looks like I should have followed the advice you gave me right when I saw that write activity, because it looks like that process did nothing else than erase my disk. A quick check with dd | od showed that the first 62 GByte of the disk are all zeros now. How much it zeroed out in the hours it ran I do not know yet.

The reason I let it run is, because I knew from my sister, which had probably a cable that wasn't sound and thus her disk ejected quite often, that interrupting recovery process when a drive is freshly connected to the computer could result in it becoming corrupted to the point that it macOS will then allow it only to be read and not written anymore.

In hindsight though I should have taken that risk, as read/onl is still better then loosing the data.

I'm still wondering though how that could have happened. After that I started my computer in recovery mode and ran a visor check on my laptops disk to see if that could have been the cause, but no viruses found.

Oh well.

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Answer 5

claudio1961 Author

Level 1

8 points

May 31, 2020 11:28 AM in response to Kappy

Hi,

thanks I'll try that.

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diskmanagementd writing to external disk which is not yet mounted

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