GT said:
Following on from Bob L's post and a few others. I have also bought a
reported 16GB flash drive from ebay. I expected it to be a fake, but it
looked like and actually is a very nice looking device - leather bound with
an aluminium lid. It seems to hold about 3-4GB before corrupting further
data. Even at that capacity, it was a bargain and I can't really complain,
given the price. I have 2 Questions:
1. How do they fake these things - do they have genuine memory chips, but
somehow report a false total?
2. How reliable is any data that we do manage to save to the drives?
GT
I have no idea what's going on inside, but I have studied the external
effects extensively.
Near as I can tell, the FAT or MFT has the correct memory map when
looking at the input side. But the output seems to wrap at the end
of the real flash and start
overwriting previous data. The directory is correct, the map points to
the place
the file was written, but parts of the file may have been overwritten by
newer cross-linked data. Most recently written data is probably ok.
There are other factors that come into play. There's a process for
mapping out bad memory and pointing to replacement memory. There may
be wear leveling algorithms that put the data other than where
you'd expect a linear write to go.
The operating system complicates the testing process. If you write a
bunch of files to the flash drive, then read it back, it WILL compare
favorably with the original files....because the operating system is not
reading the flash...it's giving you back the write cache. So, you put your
most precious pictures on the drive a batch at a time and they read back
fine. But later, when you try to show them to someone, they're corrupt.
I expect that most people with fake flash don't even know it.
By the time you find out, it's too late to return it.
The actual return rate is low enough that the sellers can stay
in business.
I have only one fake flash drive. The drive reports itself as 16GB, but
the chip inside is 32MB...yes megabytes.
Just writing a smaller amount of data won't save you. The drive
is gonna wrap whether you delete old files or not.
I attempted to partition the drive so I could use the good 32MB. It
seemed to work at first, but eventually started getting cross-linked
files. I wouldn't risk any data I cared about on one.
I tried to buy three drives locally off Craigslist. ALL of them were
fake. And the sellers acted like they knew it. There are only two
things to do with a fake flash.
sell it on ebay
sell it on Craigslist
Starts with chinese imports, but propagates thru used channels.
It was reported that the clever sellers price drives a penny cheaper
than the amount required for Paypal/ebay buyer protection.
So, how do you test a flash drive? You fill it to the brim. You
unplug/dismount it to clear the OS file cache.
You plug it back in. Then you do a bit/bit compare of the flash files
with the original files.
Do the math...
If you take your usb1.1 laptop to the seller and attempt to test a 16GB
flash drive, two things will happen.
1) The seller will be pissed and throw you out.
2) Your battery will be dead long before the test is done.
Turns out that a USB2.0 port won't help you check the size, because one
of the symptoms
of a fake flash is VERY slow write speed. But if you measure the write
speed, you won't want the drive even if the size checks out...so it
helps to have a fast USB port.
One local guy who deals in fake flash on Craigslist advertises drives as
high-speed actual write speed of 5Mbps. Turns out it's not a typo.
They really are that slow...and they're fake.
I wrote a program to test flash drives. It fills up the drive without
actually writing all the data. Takes only a few minutes to run and has
a high probability of finding a fake drive. Problem is that I have only
one fake drive to test it on. And it tricks the operating
system, so if it crashes, I'd be worried hozing the hard drive.
Doesn't do any good if you can't get access to the drive before you buy it.
It's less an issue when you can get new 16GB drives from Fry's for $10
after rebate.
Are we having fun yet?
mike
