It's no different than any other part of the drive as far as holding data, except neither the OS or you are allowed to touch it. Whether it succeeds or not, there is a small area of the drive set aside for mapping out bad blocks/sectors. When you have bad blocks/sectors on a drive, the drive's own firmware will attempt to move the data in the corrupt area of the drive to a new location. It can't create more from out of nowhere. A drive has as many sectors on it that it will ever have when it ships from the factory. Sector replacement is a highly incorrect term that you'll find all over the web. And for the typical user, even a one pass erase is as good as gone.
There is virtually nothing that can recover anything from a seven pass erase. When you do a Secure Empty Trash, the areas of the drive where the data is stored are overwritten seven times with random data. When you secure erase an entire rotating hard drive with Disk Utility, it actually does overwrite each sector/block for as many passes as you choose. To note, sector replacement regarding hard drives has nothing to do with erasing the data on them. No need to write any zeros and shorten the life of the SSD. With SSDs, it is better to operate them full time as FileVault encrypted drives and then as Barney-15E suggests, just do a reformat which will throw away the old encryption key and then sectors will just be a bunch of random bits. The SSD does wear leveling to help avoid this, but zeroing an entire SSD (or worse 7 or 35 pass random patterns), can seriously reduce the life of the SSD. SSDs have a limited number of writes per sector before the material physically wears out. As a result it is not wise to declare something 'secure' when it isn't.įinally, writing zeros on an SSD, besides not actually zeroing what you think you are zeroing (as in it can leave a few gigabytes of your original data still accessible), the zeroing also shortens the life of the SSD. And since erasing an external drive was your stated goal, why didn't you select an external drive instead of your internal Apple SSD?Īnd Disk Utility is not going to knowingly erase the boot drive, which it appears you have selected for you screen shot.Īnd it turns out disk drives and SSDs make it extremely difficult to perform a true guaranteed secure erase, as the rotating devices perform sector replacement where knowledgeable individuals can recover data from it after a secure erase, and SSDs never write to the sector where the data is stored, then always write to a new sector, and must move the original sector to a garbage collection area, where again knowledgeable individuals can recover your data.
Disk Utility is not showing me an obvious place to find an option to Secure Erase (zero out) an external hard drive.
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