Check fake flash drives and set them to their real sizes

Question

I have a couple hundred of "fake" flash drives; The kind you would see on online store, with false/questioning sizes, like "1TB" or "1ZB"...

How do i know they are "fake"? They basically stop the transfer of files after some point, where they basically fail and the OS where the transfer happen usually show an error.

Now i did manage to check for the real size of such flash drive, and set them to their real size, a while ago (couple years ago, so i don't remember the exact procedure), but i did so:

• Fill flash drive until error come up, and note down/print the actual/exact size of said data when the error comes up (since it would indicate the real size of said flash drive).
• "format" the flash drive to it's real size, by using dd.

I'm already partially aware on how to do the first part. The problem comes at the second part, which I'm not entirely sure how it is done, though i do remember that back then, when i did it, i used dd to write an empty image file i created, of the exact, real size of the flash drive, and used dd with it.

Some might think/argue that, "it is useless" or "the effort outweigh the result", which might be true if i only had one or two of these, but given that i always can find a use for these flash drives, even if not practical (due to the amount), it doesn't mean it's useless.

It is also possible given i managed to do it once, though i forgot about it...(and others probably managed to do something similar, though i didn't find any such examples on linux)

I don't have any data on these, and i also do not care if they break (given the amount i have) but i would still prefer setting them to their real size, as previously stated.

I basically want to do all of this with bash, dd, and some other Posix utilities.

Answer 1

You can use the tool f3 for this. It is a linux-port of H2testw (german).

F3 is included in most major Distributions like debian, ubuntu and fedora

EDIT: you cannot fix the size of the stick/card/whatever without changing the firmware which is not a trivial task. But f3 provides the command f3fix which creates a partition with the real size of the stick so you cannot “overcommit” data by accident.

Answer 2

1. Use dd (badblocks in read-write mode with a test pattern could be a much better option) to wipe them and write down the real size.
2. Use fdisk/gdisk/sfdisk/cfdisk/whatever to create a single partition of the right use. Most of them can be trivially automated - probably the easiest one would be sfdisk /dev/device < partition_table_file.