External hard drive format changed overnight!

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Level 1

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External hard drive format changed overnight!

I copied a whole load of image files onto an external hard drive that has only ever been used with a Mac, the other day. Then, yesterday, I relocated about 20,000 Aperture previews from a legacy library onto the drive (in preparation for losing Aperture with Catalina)

I left it running overnight and noticed in the morning I had the 'disk not ejected properly message', and the external drive had de-mounted.

However, it now won't mount again and Disk Utility says it can't do First Aid on it or Mount it either. The drive itself is shown as mounted and First Aid shows no problems, but the Volume can't be either mounted or repaired.

I then noticed it says the 'Volume' is formatted as MS-DOS (32 Bit)!!! As I say, this drive has never been used on a Windows PC as far as I can recall, so how can this have happened?

(It is quite an old drive that I suspect I formatted for Mac myself originally, from its default Windows format)

I have just found a Windows PC and am able to read the drive and am taking files off it, right now, but is there any way to change the formatting of the drive back to Mac, without deleting the whole drive and having to start again? (It took about 8 hours to do first time around!)

MacBook Pro 15", macOS 10.14

Posted on Nov 13, 2019 5:49 AM

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Answer 1

Top-ranking reply

Eau Rouge

Level 8

42,590 points

Nov 13, 2019 6:23 AM in response to Vapresto

At the end of the day do you want this drive to be used on both Macs and Windows PC's

if so you will need to format it differently as to my suggestion earlier. My method will

format the disk for Macs only.

If you would like to share it between Macs and PC's then

change Format to exFAT and Scheme to Master Boot Record.

(the exFAT format has no limit on individual file size, whereas MS-DOS FAT32

has a file limit size of 4GBs.)

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Answer 2

Eau Rouge

Level 8

42,590 points

Nov 13, 2019 5:58 AM in response to Vapresto

If you wanted to reformat the disk back to a Mac Format then you would need to copy the files off of the disk.

formatting the drive erases the disk.

When you open Disk Utility, click on View in the menubar and select Show All Devices.

In the left of the Disk Utility window highlight the Disk not the indented Volume.

click on Erase, give the Disk a name, Format Mac OS Extended (Journaled)

and Scheme, GUID Partition Map. Click Erase.

See below.

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Answer 3

JimmyCMPIT

Level 7

29,258 points

Nov 13, 2019 6:00 AM in response to Vapresto

many external drives are formatted FAT32 at the factory, especially the ones that are Windows/Mac compatible. Unless you definitely reformatted the drive on a macOS to a "mac" format then FAT32 should be readable/writable on a mac, no benefit, but usable.

FAT to NFTS without reformat is possible (NFTS to FAT is not BTW) but FAT to a Mac/Unix format requires you to reformat, however it sounds like the drive or the cable is having issues, not the format.

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Answer 4

Vapresto Author

Level 1

22 points

Nov 13, 2019 6:12 AM in response to Vapresto

That all sounds plausible and it is possible that I didn't bother to reformat it, if it just worked as it was - thank you.

Still strange that it appears not to have any issues with Windows? Maybe it's the file that Apple uses to recognise the drive that's corrupt? and not affected by windows? I'm not a techie, I'm afraid so don't really understand what I'm saying, I'm afraid!

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External hard drive format changed overnight!

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