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Hi! my question has 2 parts. Is erasing the HD a secure way to really delete your info? It seems so but I’d like to make sure. Also, I have a late 2011 MacBook Pro. If I erase the HD do I need a disc to reinstall?
MacBook Pro
Hi AliciaHa,
1. Although more passes may make an erase more "secure", some drives can survive these types of erasure. To truly erase your data securely, first encrypt the hard drive in question (assuming that it's formatted as Mac OS Extended Journaled or APFS). If the hard drive in question is your internal drive, turn on FileVault and wait for encryption to complete before you erase your drive. Once the drive is encrypted it doesn't matter how many passes you choose to do, since once the encryption keys are gone it's impossible to recover the data.
2. Depends on when your Mac was manufactured. If it came with an install disc, you'll need to use it if you erase the entire drive and not just your startup partition (which contains your data). If your Mac didn't come with an install disc, you can boot Recovery Mode over the Internet using one of these key combinations at startup:
If your Mac has macOS Sierra or later:
Option-Command-R to boot latest (non-beta) version of Recovery Mode
Shift-Option-Command-R to boot version of Recovery Mode that shipped with your Mac
If your Mac has OS X El Capitan or earlier:
Option-Command-R to boot version of Recovery Mode that shipped with your Mac
More info about Recovery Mode can be found in the links below:
Hi AliciaHa,
1. Although more passes may make an erase more "secure", some drives can survive these types of erasure. To truly erase your data securely, first encrypt the hard drive in question (assuming that it's formatted as Mac OS Extended Journaled or APFS). If the hard drive in question is your internal drive, turn on FileVault and wait for encryption to complete before you erase your drive. Once the drive is encrypted it doesn't matter how many passes you choose to do, since once the encryption keys are gone it's impossible to recover the data.
2. Depends on when your Mac was manufactured. If it came with an install disc, you'll need to use it if you erase the entire drive and not just your startup partition (which contains your data). If your Mac didn't come with an install disc, you can boot Recovery Mode over the Internet using one of these key combinations at startup:
If your Mac has macOS Sierra or later:
Option-Command-R to boot latest (non-beta) version of Recovery Mode
Shift-Option-Command-R to boot version of Recovery Mode that shipped with your Mac
If your Mac has OS X El Capitan or earlier:
Option-Command-R to boot version of Recovery Mode that shipped with your Mac
More info about Recovery Mode can be found in the links below:
About macOS Recovery - http://support.apple.com/kb/HT4718 - "OS X Lion and later include OS X Recovery. This feature includes all of the tools you need to reinstall OS X, repair your disk, and even restore from a Time Machine backup." - Also information about Internet recovery.
Of course if you erase an entire hard drive it will probably wipe out the recovery partition.
How secure do you really need?
If you Mac has nuclear secrets, a 10-pass erase with different random data each time will probably finish in under a week of constant writing.
But if you just want to get rid of your stuff and you do not anticipate the drive will be physically seized by forces hostile to you, a simple erase (which clears only the Directory, and adds the data blocks up to the Free List for re-use over time) will suffice. It will finish in about a minute. A re-Install of MacOS will write about 350,000 files.
1. It depends on whether you did a secure or regular erasure. Doing more passes will make the data harder to recover but also causes the process to take longer.
2. No.
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Is erasing the hard drive secure? do I need a disc to reinstall OS?
