SD Cards, refurbished, upgraded

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I'm still bemused that so many sellers are offering refurbished and  
upgraded SD cards at rock-bottom prices, but are still getting away  
with blatant untruths - or am I wrong?

I have recently purchased a 128GB one for 6GBP which the Windows app  
h2testw showed having a shortfall of 7.7GB, which is a lot better than  
expected, but one wonders how reliable the card might be.

Thoughts anyone?

--  
Mark J
From RISCOS on a BeagleBoard-xM and Raspberry Pi2B
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Re: SD Cards, refurbished, upgraded
On 5/6/2015 1:49 AM, Mark J wrote:
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I don't have any first hand experience with this but the defects on a  
flash chip are statistical.  If they allow for say, 10 defects on the  
die and 95% of the time the devices meet this standard, there will be 5%  
that don't and end up on the grey market.  I would not expect these  
devices to be any worse in terms of reliability.  They just ended up  
with more than their fair share of the spot defects.

--  

Rick

Re: SD Cards, refurbished, upgraded

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They'll normally get away with it -- but such SD cards could indeed be a
particular problem for the Pi.

SD-cards have a processor that rapidly remaps blocks of physical memory
in and out of the address space because partial-block writes can not be
done to the physical memory.  A physical memory block can only be
written to without corruption if it is completely cleared first. The
actual partial-block write process is: read from an existing block,
merge with the new data, write to a cleared block, and remap that into
the address space.  If a card has too many physical memory defects, then
it'll be firmware-programmed to be a smaller size so that it still has a
sufficient margin of spare blocks that can be switched around as the
data-writes occur.

It's known that some vendors (especially Chinese vendors) will "upgrade"
these SD-cards back to their original size.  This will *probably* be OK
if the cards are used in a camera (their main use) because the writes
are typically slow and are writes to whole blocks. However, these cards
might not have enough spare blocks left to meet the timing requirements
that the card's original designer intended, so rapid small-file
(partial-block) writes might cause corruption as the cards's processor
is unable to find the expected number of erased blocks for its normal
operation.  Thus such a card might work fine in a camera but become
corrupted by the Pi, and become corrupted in a way that causes it to
lose track of which physical blocks are erased, so even remaking its
filesystem might not fix the corruption.

  

Re: SD Cards, refurbished, upgraded
On Wed, 06 May 2015 06:49:43 +0100, Mark J

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    There is also the matter of whether they are advertising using decimal
GB or binary GB...  

128,000,000,000 vs 137,438,953,472 -- a difference of 9+GB
--  
    Wulfraed                 Dennis Lee Bieber         AF6VN
     snipped-for-privacy@ix.netcom.com    HTTP://wlfraed.home.netcom.com/

Re: SD Cards, refurbished, upgraded
On 5/6/2015 8:56 AM, Dennis Lee Bieber wrote:
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It's *always* decimal GB.

--  

Rick

Re: SD Cards, refurbished, upgraded

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The label is always decimal, but Windows reports binary, hence showing  
apparently significantly less than advertised.

--  
Alan Adams, from Northamptonshire
snipped-for-privacy@adamshome.org.uk
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Re: SD Cards, refurbished, upgraded
On 5/6/2015 12:05 PM, Alan Adams wrote:
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Windows reports both.  Choose your poison.

--  

Rick

Re: SD Cards, refurbished, upgraded

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Only a question. Does anybody have a list of companies that actually
manufacturer SD cards? I know that even if I buy something from say,
Samsung, it may be a fake but at least I will cut out the risk of
buying a rebranded factory second.  

Re: SD Cards, refurbished, upgraded
On 5/6/2015 11:28 AM, Gordon Levi wrote:
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I don't know for sure, but I expect most fakes *are* factory seconds.

--  

Rick

Re: SD Cards, refurbished, upgraded

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- if I, as the OP, can come back here (with thanks to rickman and all  
others for taking me seriously)...

I had misread the h2testw result, and had not realised how the running  
of the app can be upset by what else the Windows box was trying to do  
at the same time (The device is not ready. Code 21), so re-ran it  
(something like six hours to write and verify) after Windows had  
properly settled down. The result, hopefully not unhelpfully  
formatted, is below:

The media is likely to be defective.
7.7 GByte OK (16205824 sectors)
113.2 GByte DATA LOST (237576192 sectors)
0 KByte overwritten (0 sectors)
0 KByte slightly changed (< 8 bit/sector, 0 sectors)
113.2 GByte corrupted (237576192 sectors)
0 KByte aliased memory (0 sectors)
First error at offset: 0x00000001ee900000
Expected: 0x00000001ee900000
Found: 0x0000000000000000
H2testw version 1.3
Writing speed: 10.4 MByte/s
Reading speed: 9.14 MByte/s
H2testw v1.4

It means very little to me, other than the obvious that the card is  
defective, and is 7.7GB usueable, not 7.7GB short as I originally  
misunderstood, and far short of the 128GB Class 10 unbranded  
upgraded/refurbished as sold - and 125GB or 134GB or thereabouts  
decimal/binary as Windows reported.

Confusingly, to my mind, the card has 121 notionally 1.1GB h2testw  
files, plus a single 13.6MB one to round off with. That probably  
caused me to misread 7.7GB as defective/useable. The .h2w filetype  
appears unreadable under Windows XP, Ubuntu on the Panda, or RISCOS on  
this Beagle, but a cursory look at Properties suggests that the 121  
are all the same size - presumably because the many errors have been  
padded over.

As one who started out thinking a C60 was magic, a MicroSD still seems  
a total hoot! What on earth will be the norm in another 30 years...

Thanks very much for the informed opinion and observations from all. I  
will now return to what I do understand, if I can remember what that  
is...


--  
Mark J
From RISCOS on a BeagleBoard-xM and Raspberry Pi2B
We've slightly trimmed the long signature. Click to see the full one.
Re: SD Cards, refurbished, upgraded
Mark J wrote:

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Local file storage will be probably be illegal by then ;)

fruit

Re: SD Cards, refurbished, upgraded
On 07/05/15 06:53, Mark J wrote:
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It looks like it is an 8GB card that has been programmed to report
128GB :(


Re: SD Cards, refurbished, upgraded

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Well, that's the upgrade. Presumably repainting the outside to 128GB  
was the refurbishment!

--  
Mark J
From RISCOS on a BeagleBoard-xM and Raspberry Pi2B
We've slightly trimmed the long signature. Click to see the full one.
Re: SD Cards, refurbished, upgraded


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Was it a Chinese Ebay vendor? :)

You can get good stuff from Chinese Ebay vendors, but I recommend only
choosing those that have clocked up several thousand sales and have >99%
positive feedback.

Re: SD Cards, refurbished, upgraded
On Thu, 07 May 2015 06:53:14 +0100, Mark J

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    And seems to have a faster write speed than read speed -- which is not
normal either.

    I'd also be perplexed at that "first error at...", "expected..." set...
What is it doing, writing 64-bit addresses AS the data?

--  
    Wulfraed                 Dennis Lee Bieber         AF6VN
     snipped-for-privacy@ix.netcom.com    HTTP://wlfraed.home.netcom.com/

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