USB card reader problem

[Colin Law]

On 13 August 2015 at 09:56, Tony Baechler <bats at batsupport.com> wrote:
> Hi all,
>
> I'm wondering if this is a hardware problem or if I'm doing something wrong.
> It isn't a big issue, but it has been annoying me for a few years now and is
> more a matter of curiosity.
>
> I have a multiboot setup here.  On sda1, I have Windows XP.  On sda2, I have
> a new install of Ubuntu MATE 15.04.  On sda3, I have Debian testing with
> kernel 2.6.32.  Newer kernels don't support my serial device.
>
> If I turn on the machine and plug in my USB card reader with an SD card
> inserted before the machine boots, the kernel usually sees it and outputs a
> message recognizing it.  I can mount it as normal, copy files to it, etc.
> Most of the time, copying files is fast.  It takes a few seconds to copy 100
> MB.  Obviously it doesn't write to the card that fast because there is a
> long delay when I unmount it.  The same process takes about 10 minutes on
> Windows.
>
> Every once in a while, especially if the system is already booted before I
> plug in the card reader, it's very slow.  It's at least as slow as Windows.
> If I plug in the reader before the system boots, that usually doesn't
> happen.  Thinking it might be a kernel problem since 2.6.32 is very old, I
> thought I would try with Ubuntu MATE and kernel 3.19.  I had the same
> problem.  It was immediately recognized, but copying from the console was
> very slow.  Thinking it might have to do with the desktop automounting it, I
> unmounted it from the console and remounted it temporarily under /opt. There
> was no improvement.

That sounds as if it might be something to do with the way the writes
are being buffered.  You said even when it appears to write fast that
you then had to wait when unmounting, so likely the actual speed
writing to the device is the same whether it appears to be fast or
slow, but for some reason sometimes it is insisting on writing
directly to the device rather than through buffers.

Please copy/paste the relevant contents of syslog when you plug in the
card in the case where it turns out to be slow and the same when it is
fast.  Then the first question is whether there is a difference.

Colin