iMac not recognising Samsung SSD; Error code -69854

Question

iMac not recognising Samsung SSD; Error code -69854

iMAc Late 2015

Monterey 12.7.6

I'm trying to (re-)connect my Samsung portable SSD to my iMac. It's previously worked fine for Time Machine backups. The drive doesn't show up in Finder (and I have already set Finder preferences to show external drives so please don't suggest that!).

The drive does show up in Disk Utility, but can't be accessed by Time Machine. When I try 'Information' in disk utility everything looks OK (see below) but First Aid fails with the following messages (see below):-

Problems were found with the partition map which might prevent booting

A disk with a mount point is required : (-69854)

Earlier Mac models

Posted on Aug 22, 2026 3:35 AM

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Answer 1

Aug 23, 2026 9:54 AM in response to Philip the Aussie

Did you run First Aid on the hidden Container?

If there are any errors/warnings, then run First Aid again until they are gone. If after several scans the errors/warnings remain, then it is not possible to fix the file system.

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Answer 2

Aug 22, 2026 7:50 AM in response to Philip the Aussie

Philip the Aussie wrote:

... First Aid fails with the following messages (see below):-

Problems were found with the partition map which might prevent booting

A disk with a mount point is required : (-69854)

Sounds like an erase and reformat is in order.

A backup isn't a backup unless one has multiple copies.

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