Hi,
I know that performing a "Surface Scan" on a HD (hard disk) via
"ScanDisk" was useful in finding a bad sector(s), but I wonder if performing a
"Surface Scan" on a USB flash drive will expose an integrity flaw?
Thank You in advance, John
The USB Flash should have much the same facilities as a hard drive.
On a hard drive, a bad sector is spared out automatically.
When there are no longer spares available near the bad sector,
the sector is then "really bad". An attempt to read the bad
sector then, returns a CRC error. And the OS may then get to
add the bad cluster, to a bad cluster list.
So surface scanning the hard drive, doesn't necessarily expose the
"problem" in a useful way. Only when it's almost too late, does
your first bad cluster show up. Using S.M.A.R.T statistics and
reallocated sectors, you get an earlier indication, but even
then, I suspect up to a certain level of usage of spares,
the stats will show nothing. (If the scale was perfectly linear,
users could "cherry pick" hard drives, and send back any drive
showing even one error. By preventing the stats from showing
low numbers of errors, the user cannot figure out whether to
keep the drive or send it back.)
A USB flash, could have sparing at the block level. And an error
detecting code, can tell when a block has correctable errors,
or so many errors as to be uncorrectable. Unfortunately, the
documentation for flash controllers and chips, isn't good enough
to develop a more detailed picture of how it all works.
I don't think a USB flash has S.M.A.R.T, so you don't have that
to work with either.
If you surface scan the USB flash, it's going to look "perfect",
up until the day it runs out of spare blocks, and in all probability,
it'll die the same day. So it's not like there would be a long
interval between "spotting trouble" and "it's dead Jim".
You would need a utility that can "reach the flash chips"
and talk to them directly. And get info about how many blocks
are currently spared out. The manufacturer may have such a
utility, but they're not generally shared with the public.
One indicator of health, might be access speed, but I don't
have any useful information on how to relate the two. I feel
a flash stick that is slowing down, isn't healthy, but I can't
tell you how many days are left if it is running at about half
speed.
I guess this is why I would recommend a USB flash for "data transport"
but not for "archival storage". Never put your only copy of some
data, on USB flash.
Paul