Jimmy Wilkinson Knife wrote:


Maybe that's why mine are slowing down - more cells are becoming weak?

The Toolkit software that comes with the drive,
should be able to provide statistics for you.
Like, how many blocks were spared out. If a block
cannot remember what you write to it, the drive
may decide to spare it out and replace it, just
like a hard drive would. This is automatic sparing
just like in the ATA designs.

The kind of "weak" I'm referring to, is not permanently
damaged sectors. It's sectors that the charge is
draining off the floating gates in a matter of
a few months, rather than the ten years we would
normally expect. This was causing the read rate
on "data at rest" to drop. So if you wrote a backup
today on the device, it might read at 300MB/sec. If
two months from now, you tried to read the same big file
again, it would be reading at 180MB/sec. And it
does that, because the charge draining off the cells
corrupts them, and the powerful error correcting code
needs time to do the corrections to multiple bits
in the sector. The data is still officially "intact"
and error free, in that the error corrector isn't exhausted.

They "fixed" this in a firmware update, by having the
drive re-write the cells after three months (equals
degraded wear life and shortens the life of the drive).

On TLC, around 10% of storage is used for ECC bits, and
when QLC comes out, this is expected to grow.

At some point, adding ECC will affect storage capacity
sufficiently, we will have hit a wall on "extending the
number of bits stored in one cell". For example, if
you needed as many ECC bits as data stored, yes, you
doubled the capacity by going from QLC to the next thing,
but you cut the capacity in half by the need to use more ECC.
They can't keep increasing the bits per cell before
it bites them on the ass. The write cycles is dropping
with each generation too. Flash is becoming the equivalent
of silicon toilet paper.

In fact, doing some math the other day, I figured out
it was costing me $1 to write a Flash drive from
one end to the other. There is a tangible wearout
on the highest density devices. And it's beginning
to equate to dollars. When I use a hard drive on the
other hand, I don't have such a notion. It's been
a long time since I lost a hard drive. I've got
a few that have bad SMART, but "they're not dead yet".
Some of the flaky ones have been going for an extra
five years after retirement (now used as scratch drives).

There are just a few flash drives, that are huge and
the interface happens to be slow. There's a 30TB one,
you can continuously write it at the full rate, and it
is guaranteed to pass the warranty period :-)
So that would be an example of a drive, where
a lab accident can't destroy it. Because it
can handle the wear life of writing continuously
at its full speed (of maybe 300 to 400MB/sec).
If the 30TB drive was NVMe format, and ran at
2500MB/sec, it might not be able to brag about
supporting continuous write for the entire warranty
period. You might have to stop writing it once in
a while :-)

Paul