On 3/12/19 3:43 AM, Paul wrote:
T wrote:
On 3/12/19 1:48 AM, T wrote:
On 3/12/19 1:28 AM, Paul wrote:
Mike was referring to "trial" of a LiveDVD without installation.

You can't trial every possible thing from a LiveDVD, unless
you set up a persistent store.

True and an art form in its own.

This is typically done on
LiveDVDs transferred to USB sticks, where a 4GB persistence
file ("casper-rw") is added to the USB key, so that more
extensive procedures can be tried. Such as installing the
NVidia graphics driver, trying VirtualBox or VMPlayer.

Not everyone has scratch drives for installing Linux for testing.
I have a ton of drives, and you can never really have enough
drives for this sort of testing. For example, right now, when
I'm finished with the 500GB HDD in the Test Machine, I have
to restore from backup, to put the previous experiment back
on there.

But a lot of us have Flash drives kicking around.Â* And you can
install to them and test whatever you want.

The best flash drive for this I have found are from Samsung.
No troubles with massive small file transfers.Â* Patriot
are the worst.


Install from a Live USB to a Sumsung flash drive in a USB 3.1/C
jack and it will give Windows a run for its money performance wise.
I have actually had them go faster in some customer's machines.


This is bad advice.

I've ruined two USB keys doing exactly that.

No more USB keys will be used here for either
persistent store or for install as slash.

When the first one failed, I pretended it was
a fluke. When the second one failed not too much
longer after that, I stopped pretending.

If it needs storage, it goes on a HDD. One
of the scratch HDDs (I probably have five or six
500GB ones for this, some are scratch because
of the danger they might fail). Even the ones
with a few reallocations showing, haven't actually
died on me yet.

The flash keys that failed, were TLC based, because
I opened up the sticks and looked up the chip numbers
in Google. If you have a stick old enough to be
based on MLC or SLC, that's probably safe for installation
purposes, just because there are more write cycles
available (even if the technology doesn't have effective
wear leveling).

If I had proof that the USB flash stick had as good
wear leveling as an SSD does, I wouldn't be nearly
as concerned. But the way these sticks fails, suggests
there is little in the way of wear leveling there. And
it could be all too easy to "burn a hole" in one as a result.
The sticks behaved slowly at first (write rate drops
to 1.5 to 3MB/sec), and it isn't that much later before
the thing disappears completely.

*******

And newer sticks are getting worse.

I bought a Sandisk Extreme maybe a year and a half ago,
and it has worked consistently.

I liked it enough, to look for such a stick at the
computer store a couple weeks ago. The model number had changed,
as you would expect.

I brought the stick home, and read speed was 50MB/sec.
That is hardly Extreme.

I tried using "dd", and did "dd if=/dev/urandom" and
used a random bit pattern to write the stick from
end to end. After that, a read test gave a more
uniform 150MB/sec on read.

So the root cause of the initial terrible performance,
is "mushy TLC" syndrome. This is where every sector
on the stick, when you get it, has errors requiring
ECC correction inside the stick. This causes the
read rate to drop, because the microcontroller inside
the chip does the correction in firmware. There isn't
a dedicated hardware block for error correction. TLC
is bad enough, theyÂ* might use 50 bytes of overhead
for every 512 bytes of data. And the poor microcontroller
then has to work out which bits in the just-read block
need to be flipped.

I'm expecting if I leave data on the new stick, then
three months from now the read rate will have dropped
to 50MB/sec again. The question then is, how long
before the 512 byte block is "uncorrectable". The 50 byte
number is assumed to be powerful enough for a certain
error rate over time. And the "mushy" behavior isn't
supposed to lead to data loss. But how warm and fuzzy
do I feel about this... Hmmm.

I have other USB sticks that are slow but consistent.
I might not have a problem using those, but because
they're slow, the experience wouldn't be all that pleasant.
Nobody enjoys consistent 3MB/sec write rates (a couple
of them had that speed from day one).

If you got some good USB sticks, then great... I fully
recommend my OCZ RALLY2 8GB, which is bulletproof (at least
compared to the pile of TLC rubbish sitting on my desk
right now). I probably bought that eight or ten years ago.
That would be a good candidate for an install. But I only
own one of those (it had a mail in rebate, one per household).

Â*Â* Paul


When I used Kanguru stick for such purposes and they corrupted
out, I did a dd from /dev/zero all over the stick and they
came back to life. Well, all but twice.

I use Kanguru's Flash Blu III (USB 3.0) 8 GB sticks for
installation media, such as Window 7 and 10. Never an issue,
but they are only used once.