USB SD-card reader recognized, but not working, on 6.1

[Chris Rees]

2009/4/10  <perryh at pluto.rain.com>:
> Polytropon <freebsd at edvax.de> wrote:
>> On Thu, 09 Apr 2009 12:47:23 -0700, perryh at pluto.rain.com wrote:
>> > It's an SD card, not a "drive", so I had not expected it to be
>> > partitioned; but yes, it is:
>> >
>> > $ ls -l /dev/da0*
>> > crw-r-----  1 root  operator    0, 244 Feb 14 15:09 /dev/da0
>> > crw-r-----  1 root  operator    0, 245 Feb 14 15:09 /dev/da0s1
>>
>> Why don't you expect this? As far as I know, if something is
>> msdosfs-formatted (read: any "Windows" readable file system,
>> FAT), it always involves a "slice device". I never found a
>> situation where access to /dev/da0 would work.
>
> My experience is exactly the reverse.  I've never before seen a
> removable-media device (floppy, Zip-drive, JAZ drive) that *did*
> have a DOS "partition" table aka BSD "slice" table.  Surely you
> would not expect a USB floppy to show up as /dev/da0s1?
>
> AFAIK the reason for creating slices is to identify sections of
> the device for use by different OS -- something often needed
> for multi-boot from a hard drive but seldom on removable media.
> I sure wasn't planning to use part of this SD card for my camera
> to store pictures on, and the rest for FreeBSD backups :)

Aha, careful. A flash drive/card is more like a removable hard drive.
Since it's so much bigger than a floppy etc (typically) it makes sense
to have a proper slice (partition) structure.

If you want to boot off a floppy, it's a different operation from
booting off a HDD for precisely this reason. Whereas a floppy isn't a
proper, 'fixed' type disk; it's a tiny thing, suitable for max ~10
files. There's no need to have the overhead of a partition table, MBR
etc. Same with CDs, booting off them involves several strange fudges
(El Torito).

Since a flash card would be a sensible thing to boot off, the
designers want it to look more like a hard drive; as well as having
the flexibility.

Chris


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