On Wed, Jul 8, 2015 at 1:48 PM, Kaza Kore <dj_kaza(a)hotmail.com> wrote:
Date: Wed, 8 Jul 2015 18:37:04 +0000
From: f.rech(a)yahoo.fr
To: dj_kaza(a)hotmail.com
Subject: Re: [LAU] OT: Bash help to check new USB keys.
It's not a full testing of a flash device I'm worried about, especially as
they are new, I just want to know they really are the size they report as
being...
Dale.
Probably GParted will tell you that,
HTH,
Fred
Except the likes of GParted, df, udisks etc are exactly what I don't trust!
I have read too many reports of people buying say a 128GB usb drive, copying
loads of data onto it and later discovering everything after say 8 or 16GB
isn't really there! Somehow they fake the part (ToC? MBR?) which the
computer reads the size of the drive from and seems (at least in Doze-land,
where most of these reports are from, but then again so is most the computer
world) that the system even reports having written the files correctly and
they show up in the table of contents and in your file explorer as you would
expect. Hence I want to actually write data until the drive is near full and
do an md5sum on the files I have written. It's only a single write of the
few thousand they should be usable for and I plan to use them predominantly
as back-up storage so I don't envisage lots of erase and re-writes over
their lifetime. Basic drive integrity isn't a worry. Being sold dodgy, fake
components which report the wrong size is.
I did wonder if doing something as simple as a full (rather than Quick)
format to the likes of ext4 might catch out something like this too...
Dale.
Programmers like to report size in gibi bytes, and manufacturers
almost always use giga bytes.
https://en.wikipedia.org/wiki/Gibibyte
There's about a 7.5% difference between the units. So, the units can
make it look like you're losing 8GB off a 128GB disk, or 16GB off a
256GB disk.
I have to explain this to people all the time... no.... the software
is wrong according to definitions, so you have to add/subtract x% to
get your command right.
So, do some math and see if you can explain the discrepancies with units.
Chuck