USB-Stick RAID and the Problem with /dev/sda1

Hi,
I installed my SheevaPlug with debian 5.0.2 and the U-Boot for booting from
SDHC-card. This configuration is working fine, but now I got a thing that I didnt understand:

After booting from SDHC-Card (and without any USB-Stick) I got a mount-point which is
named /dev/sda1 and mounted at /
But I think at / should the SDHC-Card be mounted which resides at /dev/mmcblk0(p1/p2)

The problem with this sda-Mountpoint is, when I insert a USB-Stick it also will be mounted as
/dev/sda1

I could see with "fdisk -l" the USB-Stick at /dev/sda1 with the right size,
but when I try to use /dev/sda1 together mit /dev/sdb1 as a mdadm-RAID
the stick doesnt seem to be recognized as /dev/sda1

So how can I tell debian/the sheevaplug to start the FIRST USB-Stick counting at /dev/sdb1 or
mounting (in the mountlist) / at /dev/mmcblk0(p1/p2) ?

For this time my way around the problem is to put at first a not-used USB-Stick in my external 4 Port-USB-Hub (which doesnt do anything as /dev/sda1) and then I do put my (at this time) 2
4GB USB-Sticks for a RAID as /dev/sdb1 and /dev/sdc1

With this configuration I could create and use my USB-Flashstick-RAID at the SheevaPlug USB-Port
which gives me a 8GB /dev/md0-Device:

fdisk -l

Disk /dev/mmcblk0: 8068 MB, 8068268032 bytes
233 heads, 20 sectors/track, 3381 cylinders
Units = cylinders of 4660 * 512 = 2385920 bytes
Disk identifier: 0x00000000

Device Boot Start End Blocks Id System
/dev/mmcblk0p1 * 1 3100 7222990 83 Linux
/dev/mmcblk0p2 3101 3381 654730 82 Linux
swap / Solaris

Disk /dev/sda: 259 MB, 259522560 bytes
255 heads, 63 sectors/track, 31 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x00000000

Device Boot Start End Blocks Id System
/dev/sda1 1 32 253386 b W95 FAT32
Partition 1 has different physical/logical endings:
phys=(1023, 254, 63) logical=(31, 139, 63)

Disk /dev/sdb: 4007 MB, 4007624704 bytes
32 heads, 63 sectors/track, 3882 cylinders
Units = cylinders of 2016 * 512 = 1032192 bytes
Disk identifier: 0x740f1bbe

Device Boot Start End Blocks Id System
/dev/sdb1 1 3882 3913024+ b W95 FAT32

Disk /dev/sdc: 4007 MB, 4007624704 bytes
32 heads, 63 sectors/track, 3882 cylinders
Units = cylinders of 2016 * 512 = 1032192 bytes
Disk identifier: 0x14e965e0

Device Boot Start End Blocks Id System
/dev/sdc1 1 3882 3913024+ b W95 FAT32

Disk /dev/md0: 8013 MB, 8013742080 bytes
2 heads, 4 sectors/track, 1956480 cylinders
Units = cylinders of 8 * 512 = 4096 bytes
Disk identifier: 0x00000000

Disk /dev/md0 doesn't contain a valid partition table

BTW: I dont know why the partition-tabel at /dev/md0 shouldnt be OK.
A fsck for this device did show that the device is clean.

Anybody else try to use a (USB-Stick)-Software-RAID on the Sheevaplug?

Bye
Guido