Re: [tlug] Micro-SD Card Throws Me A Curve Ball

[Godwin Stewart <gstewart@example.com>]

On Sun, 06 May 2007 00:16:02 +0900, Dave M G <martin@example.com>
wrote:

> Now I'm totally confused. What would be the difference between a
> micro-SD card and a regular sized SD card that could account for this
> difference in behavior?

The first thing that comes to mind is the partition scheme.

Some vendors treat the memory card like a hard disk. There's a
partition table and all on them and when you "format" the card, you
basically set up a filesysteom on the first partition.

Other vendors treat the card as what's known as a "superdisk". There's
no partition table and the filesystem is plonked on the device as a
whole, just like it is on a floppy disk, for example.

I have 2 miniSD cards within reach here. One has a partition table and
the other is a superdisk. If I watch my logs while inserting each of
these cards I get this:

First for the 1GB card with a partition table:

May  5 15:24:55 dragonfly kernel: scsi3 : SCSI emulation for USB Mass Storage devices
May  5 15:25:00 dragonfly kernel: scsi 3:0:0:0: Direct-Access     Multi    Flash Reader     1.00 PQ: 0 ANSI: 0
May  5 15:25:00 dragonfly kernel: SCSI device sda: 1999872 512-byte hdwr sectors (1024 MB)
May  5 15:25:00 dragonfly kernel: sda: Write Protect is off
May  5 15:25:00 dragonfly kernel: SCSI device sda: 1999872 512-byte hdwr sectors (1024 MB)
May  5 15:25:00 dragonfly kernel: sda: Write Protect is off
May  5 15:25:00 dragonfly kernel:  sda: sda1
May  5 15:25:00 dragonfly kernel: sd 3:0:0:0: Attached scsi removable disk sda

Note the last but one line that says "sda: sda1". It's showing me that
the device is /dev/sda and that there's information in the partition
table saying that there's one partition, /dev/sda1.

If I now pull this card out and plop in the 64MB superdisk card, I get
this:

May  5 15:28:06 dragonfly kernel: scsi4 : SCSI emulation for USB Mass Storage devices
May  5 15:28:11 dragonfly kernel: scsi 4:0:0:0: Direct-Access     Multi    Flash Reader     1.00 PQ: 0 ANSI: 0
May  5 15:28:12 dragonfly kernel: SCSI device sda: 124160 512-byte hdwr sectors (64 MB)
May  5 15:28:12 dragonfly kernel: sda: Write Protect is off
May  5 15:28:12 dragonfly kernel: SCSI device sda: 124160 512-byte hdwr sectors (64 MB)
May  5 15:28:12 dragonfly kernel: sda: Write Protect is off
May  5 15:28:12 dragonfly kernel:  sda:
May  5 15:28:12 dragonfly kernel: sd 4:0:0:0: Attached scsi removable disk sda

Here, the last but one line merely says "sda:". It didn't find a
partition table and thus found no partitions.

I suggest you watch your logs while performing the same experiments on
your machine. It might point you in the right direction.

--
G. Stewart - gstewart@example.com

Experience is something you don't get until just after
you need it.

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