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I recently purchased a secondhand MacBook Air for work purposes; the laptop was shipped to me with a fresh install of OS X. I do not know the prior owner or what they used the laptop for, and thus I need to verify that all software and data on the solid state drive is both erased and irrecoverable before setting up a fresh OS X install.

I plan to do the following:

Encrypt the drive currently holding the placeholder OS X system using Filevault 2 and a strong password.

Reboot to an OS X install thumb drive, and erase the hard drive using Disk Utility. I assume this will securely erasing the FileVault key, thus rendering the old data impossible to decrypt.

Reinstall Mac OS X over the old (erased) encrypted volume, and set up FileVault 2 to encrypt this new install.

Is this sufficient to ensure that no relic software or hard drive data from the old drive owner is recoverable?

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    why do you care if thier data might still be on erased parts? – dandavis Dec 29 '17 at 5:15
  • If it was, then if the drive failed and I had to do data recovery I'd get both my data and theirs. Then I'd have to sort the two, which makes more work. Better off just getting the drive as close to "factory new" as possible, and then writing to it. – user167115 Dec 29 '17 at 21:03
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    if an ssd fails, you're not recovering anything, old or new like you would hard drive platters... – dandavis Dec 29 '17 at 21:05
  • I wasn't aware of that, thanks for the clarification. – user167115 Dec 29 '17 at 21:32
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Encryption makes no sense in this context. Writing an encrypted version of the data to the media will make it strictly easier to recover the data than simply writing random data.

However since you are asking about an SSD there is an even better option. Use a tool to issue a TRIM command (or a sequence of commands) to the drive instructing it to delete all data. This is the fastest way to wipe an SSD and makes it very difficult if not impossible to recover any of the data. It should also give you better performance of the clean install you are going to perform after wiping the SSD.

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    I think ATA Security Erase would be better, since any TRIM-capable drive is likely to fully support the ATA6 standard. Plus, many devices queue TRIM commands for later erasure by the garbage collector, which can take time. – forest Dec 29 '17 at 8:03
  • Downvote. Only reasonable way to ensure data is securely erased on a SSD is to encrypt the whole drive before formatting the drive. – efr4k Jan 9 '18 at 18:29

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