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I'm trying to erase an external disk drive that I had been using as a backup disk. There are no options for me to securely erase - the option just isn't there at all.

It is currently formatted as MAC OS Extended (Journaled, Encrypted).

I have a second HDD drive that when mounted shows the security options when erasing.

Any ideas what is going on here? This is a new problem for me; I'm sure I've secure erased this disk before.

Edit: I've just noticed that the only difference between the two disks is that the one that could be securely erased is down as a 'USB External Physical Volume' whereas the disk I'm having the problems with comes up as a 'CoreStorage logical volume'. Is this the issue?

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MacOS doesn't let you do a Secure Erase on encrypted volumes because there's no point: a single erase will delete the encryption keys; and any residual data on the disk will be meaningless junk that cannot be decrypted.

Multiple zeroing of a mechanical disk can put significant stress on it and shorten its lifespan.

Similarly, MacOS doesn't let you secure erase SSDs, because that's also a pointless exercise: doing the erase doesn't actually make it more securely erased.

Why is a secure erase 'not necessary' for SSD's?

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I've found the answer, and I'm going to leave this question up in case it helps someone else.

The issue with the disk was that it had been encrypted. I needed to reformat it with no encryption for it to be recognised as a USB External Physical Volume instead of a CoreStorage logical volume. From there it can be securely erased as normal.

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