[gentoo-user] Re: problem formatting new 256 GB USB stick : alternatives

[Grant Edwards <grant.b.edwards@gmail.com>]

On 2025-02-18, Philip Webb <purslow@ca.inter.net> wrote:
> 250218 Frank Steinmetzger wrote:
>> I recommend an external USB case with an NVMe SSD inside.
>> This may not be as compact and not as cheap,
>> but they are much much much faster and probably longer-lasting
>> than any USB stick, because their flash controllers are more sophisticated
>> and the parts of higher fidelity.  A not-too-cheap NVMe will do fine,
>> as long as it’s TLC, not QLC flash.
>
> Can you explain this -- TLC/QLC -- in more detail ?

Tri-Level Cells,  Quad-Level Cells.

SLC (single-level cells)

Each "cell" consists of a capacitor (constructed as a FET with an
isolated-gate).  In the old days, the capacitor was either chared or
not: two levels.  One bit per cell.  Easy to make and reliable.  If
you want more bits, layout more cells. That means larger dies, which
means more money.

MLC (two-level cells)

OK, let's also do four different charge levels!  You get _two_ bits
per cell with the same area of silicon.  Harder to do and not quite as
reliable, so we'll add a few extra blocks of cells and make software
deal with blocks that don't work.

TLC (tri-level cells)

Hey, what if we do 8 different charge levels! Now you get 4 bits per
cell.  Even harder to do, even less reliable...


QLC (quad-level cells)

[I think you see where this is going]