How to wipe a USB drive?

[drachillix]

@pulykamell

Wouldn’t a low-level format be good enough to keep the average schmoe out? I know that with my USB thumbdrive, at least, if I just do a normal format, my recovery utilities can get at the data. If I do a low-level format, none of my recovery programs can find anything.

Granted, I’m a PC shop but I have recovered from a machine with no valid partitions. Decent software does not care about the formatting it just nitpicks the whole surface of the drive looking for patterns that look like files.

[si_blakely]

@Absolute

I don’t know - if you fill up the entire drive with data, the wear-levelling algorithm will have no choice but to use every block.

Only in a perfect world
Unless you know completely how the wear-levelling algorithm works, and it works correctly, you can’t make the assumption. Eventually, with enough overwrites, it will.

@Absolute

You could avoid the problem entirely by encrypting the data that you place on the drive, using something like Truecrypt.

TrueCrypt is great, but it requires Admin rights on a PC to install a driver for use (even in Traveller mode), as do most other encrypted USB devices.

@Pulykamell

I was under the impression that a low-level format (which takes about 2-3 minutes) completely overwrites all Flash card sectors with either 0s or 1s. This is opposed to the normal format which just seems to clear the directory and nothing else. Is my understanding incorrect?

*Low-level format *is a nebulous phrase. A Format overwrites all sectors and identifies bad sectors (remapping them), a Quick Format resets the Allocation Tables and directory entries. A Low-level format was a manufacturers supplied method of rewriting the disk and the tracking information that was used to keep the heads aligned. These utilities are no longer used with improvements to drives.

A Format may not overwrite all data on a Flash device due to the way File Systems are handled on Flash memory, and the wear-levelling system. Sectors are not static locations im the Flash, but get dynamically mapped as they get used, so one sector may get overwritten more than once, and another not at all. It is unlikely, but possible. Multiple formats will work eventually here as well, but how many is anyones guess. 2 or 3, probably.

Si

[si_blakely]

@drachillix

Granted, I’m a PC shop but I have recovered from a machine with no valid partitions. Decent software does not care about the formatting it just nitpicks the whole surface of the drive looking for patterns that look like files.

Indeed, this is true, but Flash devices are not linear sector-based devices like drives - A drive overwrites a sector, flash devices reallocate sectors to unused cells. With special tools you can get past the reallocation mechanism to the real cells, and pick through deleted and overwritten data.

Si

[CookingWithGas]

@cornflakes

I am only moderately hardware savvy, but why not throw it in the microwave for a few minutes? Thumb drives are cheap.

You may want to read the thread instead of just the subject line.

[jjimm]

Related Q: call me stupid, but how do solid-state drives store data? They’re not magnetic, are they? (And if so, wouldn’t this render the “overwrite seven times” obsolete?)

[si_blakely]

@jjimm

Related Q: call me stupid, but how do solid-state drives store data? They’re not magnetic, are they? (And if so, wouldn’t this render the “overwrite seven times” obsolete?)

Flash memory uses trapped electrons in an insulated “cell” - once it is overwritten, the data has gone, but (as I explained upthread) the wear-levelling algorithm means that rewriting a piece of data (like a file) does not mean overwriting the old data - the old cells are added to the used list and new cells allocated to the data.

Si

[gromehown]

What if you just make a sound or movie file the same size as the flashdrive, and copy that on after deleting all other content, and then deleting it?