[geeks] Flash drive questions

[Charles Shannon Hendrix]

Mon, 07 Aug 2006 @ 11:53 +0300, Geoffrey S. Mendelson said:

> On Sun, Aug 06, 2006 at 11:36:10PM -0400, Charles Shannon Hendrix wrote:
> > A flash drive goes: work work work work *DEAD*, with little warning.
> 
> Worse. It goes work work work (bit error) work-somehere-else (more bit errors)
> and so on.
> 
> For example, a DOS file system would work almost forever if you load it
> up an mount it read only. If you copy files to it and keep adding or
> expanding them the FAT would become unreadable in a few weeks.

I haven't had that particular problem so far, though I have heard others
talk about it.

Usually what I see when flash starts going bad is a big reduction in
write speed, which seems to indicate impending doom.

I know know exactly why this is, but this is how things were explained
to me, and what I read in an IEEE journal:

Flash usually fails on a write, and will try other sectors automatically
until it works, marking the bad ones.  There is evidently no way to know
which ones are bad or how many are remapped, or how many retries are
occuring.

The flash drives use a round-robin write system to avoid hitting the
same blocks all the time, to even out wear on the device, so the host
computer doesn't actually know which physical blocks are being written
anyway.

So the drive keeps retrying which gradually slows the device down, until
it finally fails hard.

It seems to me like even if their interface is primitive, you should be
able to get at least some minor diagnostics.  I know see what would be
so hard about the device telling you when it is starting to have to do a
lot of retries, etc.

-- 
shannon "AT" widomaker.com -- ["Consulting wouldn't be what it is today
without Microsoft Windows" -- Chris Pinkham]