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Missing write-protect tab on Secure Digital SD card causing read-only?

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Missing write-protect tab on Secure Digital SD card causing read-only?

Andrew Oakley-3
I understand that the write-protect tab on SD cards is optional:
 
However, when I use an SD card without a tab (no tab at all) on my Linux Ubuntu 8.04 LTS server, it mounts it as read-only (ro) and absolutely refuses to mount read-write (rw) even if the -force option is used. It will only mount cards as read-write, for cards which have a tab and where the tab is set to the "unlock" position.
 
On my MS-Windows machine (which I only otherwise use for gaming... honest) this does not happen. It obeys the spec and mounts as read-write for cards which have no tab.
 
Is this a known bug in Ubuntu 8.04 LTS, or do I just happen to have poorly designed card reader hardware that is not obeying the SD spec?
 
Googling produces lots of anecdotes but little firm evidence either way.
 
The card readers are internal 3.5" jobs, so I really don't want to pull the server apart and swap out the card reader unless I'm reasonably sure it really is likely to be the hardware. It did only cost a fiver at a computer fair, though, so cost is not the concern - just my time.
 
Andrew Oakley
Head of Software Development

Higher Education Statistics Agency (HESA)
95 Promenade, Cheltenham, Gloucestershire GL50 1HZ
T 01242 211460  F 01242 211122  W www.hesa.ac.uk
 

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Higher Education Statistics Agency Ltd (HESA) is a company limited by
guarantee, registered in England at 95 Promenade Cheltenham GL50 1HZ.
Registered No. 2766993. The members are Universities UK and GuildHE.
Registered Charity No. 1039709. Certified to ISO 9001 and ISO 27001.

HESA Services Ltd (HSL) is a wholly owned subsidiary of HESA,
registered in England at the same address. Registered No. 3109219.
_____________________________________________________________________

This outgoing email was virus scanned for HESA by MessageLabs.
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Re: Missing write-protect tab on Secure Digital SD card causing read-only?

Matthew Daubney-2
On Wed, 2009-05-20 at 10:06 +0100, Andrew Oakley wrote:

> I understand that the write-protect tab on SD cards is optional:
> http://en.wikipedia.org/wiki/Secure_Digital_card#Optional_write-protect_tab
>  
> However, when I use an SD card without a tab (no tab at all) on my
> Linux Ubuntu 8.04 LTS server, it mounts it as read-only (ro) and
> absolutely refuses to mount read-write (rw) even if the -force option
> is used. It will only mount cards as read-write, for cards which have
> a tab and where the tab is set to the "unlock" position.
>  
> On my MS-Windows machine (which I only otherwise use for gaming...
> honest) this does not happen. It obeys the spec and mounts as
> read-write for cards which have no tab.
>  
<snip>

When you insert it into your ubuntu machine can you produce a dmesg
output? I've had one or two that wouldn't mount rw because of
inconsistances in the filesystem. They mounted fine after an fsck.

-Matt Daubney


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Re: Missing write-protect tab on Secure Digital SD card causing read-only?

Andrew Oakley-3
Matthew Daubney wrote:
> On Wed, 2009-05-20 at 10:06 +0100, Andrew Oakley wrote:
> > I understand that the write-protect tab on SD cards is optional:
> > However, when I use an SD card without a tab (no tab at all) on my
> > Linux Ubuntu 8.04 LTS server, it mounts it as read-only (ro) and
> > absolutely refuses to mount read-write (rw) even if the
> When you insert it into your ubuntu machine can you produce a dmesg
> output? I've had one or two that wouldn't mount rw because of
> inconsistances in the filesystem. They mounted fine after an fsck.

Thanks. I tried the fsck, even after unmounting it failed as the device
was considered read-only. Ditto unmounting then attempting to reformat
on the Linux box, fails as read-only. I even reformated it cleanly on
the MS-Windows machine. Still Linux box complains read-only.

Therefore I'm reasonably sure that it is the notch or the lack of tab
which is causing the problem. The question is, which machine is correct;
should an SD card which has a notch, but has no tab, be considered
read-only? I'm wondering whether the card is faulty by design, since it
has a notch but no tab (ie. if the card has a notch, it should have a
tab). Or whether my card reader is faulty by design for insisting on a
tab that need not be there.

Andrew Oakley
Head of Software Development
Higher Education Statistics Agency (HESA)
95 Promenade, Cheltenham, Gloucestershire GL50 1HZ
T 01242 211460  F 01242 211122  W www.hesa.ac.uk

_____________________________________________________________________

Higher Education Statistics Agency Ltd (HESA) is a company limited by
guarantee, registered in England at 95 Promenade Cheltenham GL50 1HZ.
Registered No. 2766993. The members are Universities UK and GuildHE.
Registered Charity No. 1039709. Certified to ISO 9001 and ISO 27001.
 
HESA Services Ltd (HSL) is a wholly owned subsidiary of HESA,
registered in England at the same address. Registered No. 3109219.
_____________________________________________________________________

This outgoing email was virus scanned for HESA by MessageLabs.
_____________________________________________________________________

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Re: Missing write-protect tab on Secure Digital SD card causing read-only?

Matthew Daubney-2
On Wed, 2009-05-20 at 11:39 +0100, Andrew Oakley wrote:
<snip>

> Thanks. I tried the fsck, even after unmounting it failed as the device
> was considered read-only. Ditto unmounting then attempting to reformat
> on the Linux box, fails as read-only. I even reformated it cleanly on
> the MS-Windows machine. Still Linux box complains read-only.
>
> Therefore I'm reasonably sure that it is the notch or the lack of tab
> which is causing the problem. The question is, which machine is correct;
> should an SD card which has a notch, but has no tab, be considered
> read-only? I'm wondering whether the card is faulty by design, since it
> has a notch but no tab (ie. if the card has a notch, it should have a
> tab). Or whether my card reader is faulty by design for insisting on a
> tab that need not be there.
<snip>

Do you have another linux machine to try it on? Or a live cd to try it
on another machine with a different card reader? Whats the make/model of
the SD card? Worth finding whether it's the card or the reader that's at
fault.

-Matt Daubney

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