As usual, please attach you report.bug file.
Just:
- rerun the installer up to the issu
- plug a USB key
- go to tty
- run the "bug" command
- attach the "report.bug" file you'll found on this USB key here

Keywords: (none) => NEEDINFO

Created attachment 6634 [details]
Bug file

i don't know if it helps but some years ago before giving this machine ( that i now got back ) it passed to install a mga1 ( but didn't worked since ).

That's not the error your logs are showing:
* error: unknown partition table format on disk /dev/sdb at /usr/lib/libDrakX/partition_table.pm line 255.

(which is a MBR one according to fdisk)

Can you try the live ISO, alter /usr/lib/libDrakX/partition_table/raw.pm:
After  line 244, which is:
    my ($pt, $info) = eval { $hd->read_one(0) };
insert the following line :
use Data::Dumper; warn Data::Dumper->Dump([ $hd, $pt, $info ], [ qw(hd pt info) ]);

Then run diskdrake&>/tmp/out.txt then attach your /tmp/out.txt file here.

Also first insert (before the Dumper one) the following lines:
if (my $res = $@) {
   warn ">> ERROR='$err'\n";
   log::l(">> ERROR='$err'");
}

Created attachment 6639 [details]
asked debug

What kind of raid is it supposed to be?

sda seems contain a partition table with all partitions in the table being on the first disk.

It looks like the first disk was used without being in a raid and the second one just has garbage.

iirc this is RAID0, how to confirm ?

The following is a libparted error:
"Error: Impossible d'ouvrir /dev/sdb - étiquette de disque non reconnue."

Also sdb is missing from fdisk output.

Last but not least the kernel said:
"sdb: unknown partition table"

So if neither the kernel, diskdrake, libparted nor fdisk can read its partition table, I think the issue is with the disk which have a broken partition table.

Can you attach the /etc/mdadm.conf from the installed OS?

i am reinstalling debian on it to tell but seems pascal is right and tht it only installs on the sda for debian ( does not complain but treat as 2 disks and not raid ).

i am reinstalling  because i did the mistake right now to tell "yes delete the partition" to see if this would fix but it didn't.

Reducing severity as it happened on one box only and all tools agree that this sdb is unparsable.

Severity: critical => normal

iirc, from my memory in mga1 that was telling it was using raid software or something like this and was asking the permission to load something like a module.

Step i don't have anymore.

in the installer in the partitionning part i see the 2 disks, "before" only one line was shown.

Nicolas, you never mentioned what kind of RAID it should be. Soft-RAID or fake-RAID? If it's fake-RAID then does the BIOS still confirm that it's set up as RAID, not as two disks? It should need the module only when it's some kind of fake-RAID that needs kernel module to display the disks as one. Also, if it's fake-RAID then who's product is it and which modules does it need?

CC: (none) => mageia

if i new i would fix.
i provide the info asked i don't know more. 
If you need specific informations ask i will answer. 
For the bios all should be ok i never modified it.

you can decrease the priority as i can install using one disk. 
I am still available to give infos, tests for the raid fix

Well, it's still important to know which kind of RAID it is. Is there anything about it in the BIOS? If it's fake-RAID there should be some configuration for it in the BIOS and also some information who produced this hardware.

sorry this is in french but this confirm this is RAID0 : http://www.01net.com/article/298244.html

anyway look to the comment #6 for more infos about the HW ( this is a sony Vaio VGC-RC102 ).

as i needed it to work, i fixed the partition table by adding one with gparted.

but that of course doesn't close this bug as the raid part still broken :)

Nothing seems to be broken. It seems there is currently no RAID configured (probably by previous install).

Fake RAID is configured by the BIOS by just adding some information on the disks to tell the operating system that it should emulate RAID.

If you ignore it and partition one disk, the information will be overwritten and there will be no RAID until you re-create one in the BIOS.

ok so nothing wrong here ? 
When possible shouldn't the isntaller propose this ?