Card reader question

[Phil]

On 15/07/15 11:58, Robert Heller wrote:
> At Wed, 15 Jul 2015 11:21:52 +1000 "Ubuntu user technical support,  not for general discussions" <ubuntu-users at lists.ubuntu.com> wrote:
>
>>
>> Thank you for reading this.
>>
>> /dev/mmcblk0 is created whenever I plug an SD card into my laptop, as
>> expected. However, my new desktop doesn't have a card reader slot and so
>> I have to use a USB card reader. The SD card is readable with a file
>> manager but /dev/mmcblk0 is not created.
>>
>> How can I overcome this problem?
>
> How is this a problem?
>
> Note that using '/dev/<disk device name>' is somewhat depreciated, at least
> for disks with actual file systems on them.  There are other
> device-independent methods using labels, UUIDs, and so on.
>
> Yes, for low-level mucking around -- eg (re-)partitioning and making new file
> systems on (new) partitions or otherwise doing direct low-level access to the
> raw bare device, one does end up using raw device names, but since you are
> talking about something that shows up with a file-manager window, this is not
> the level you are working at. Or is it?
>
> As to your 'problem': appearently directly connected SD card interface devices
> use a device driver that uses the /dev/mmcblk<Mumble> device file(s).  OTOH,
> the standard USB mass storage sub-system, used by *all* USB-based mass storage
> devices, including thumb drives, USB <=> SATA, USB <=> PATA, and USB <=> Card
> Readers, uses the SCSI disk abstraction devices (/dev/sd<Mumble>.  Ultimately,
> the device abstraction layer and the device files used have to do with how the
> device driver for the partitular hardware is written.  Since USB has a
> standard device class for devices that implement USB Mass Storage, there is a
> single driver that works with all such devices and that driver uses the SCSI
> disk abstraction driver.
>
> I *guess* it might be possible to write a clever UDEV rule that did a rename
> to /dev/mmcblk<Mumble>, for USB mass storage device(s) that matched the
> Vendor ID/Product ID of your USB card reader(s), if there is some really
> pressing reason why you absolutely, positively, must have your SD cards show
> up as /dev/mmcblk<Mumble>.
>

Thank you Robert for your detailed reply. I suspected that my problem is 
caused by the USB interface.

I have, in the past, used dd to backup my Raspberry Pi SD cards. Perhaps 
I should investigate another method.


-- 
Regards,
Phil