Grub-install fails on the RAID0 array

So I installed mdadm, created RAID0 array from two SSDs on the Asus EEE PC 901 and tried to install the system on it.
All went fine except installing grub. grub-install command does not support two disks as the arguments, but Ubiquity run
# grub-install /dev/sda /dev/sdb

Here are the commands which fixed the situation after booting second time from USB:

# apt-get install mdadm --no-install-recommends
( or
$ sudo dpkg -i /media/TMP/mdadm_3.1.4-1+8efb9d1ubuntu5_i386.deb
 in my case )
# mdadm --assemble --scan
# mdadm --assemble --run /dev/md/raidtest
(raidtest is the array name)

# mount /dev/md127p1 /mnt
# mount -t proc none /mnt/proc
# mount --bind /dev /mnt/dev
# mount --bind /sys /mnt/sys
( maybe # cp /media/TMP/mdadm_3.1.4-1+8efb9d1ubuntu5_i386.deb /mnt/ )
# chroot /mnt

# apt-get install mdadm --no-install-recommends
( or # dpkg -i mdadm_3.1.4-1+8efb9d1ubuntu5_i386.deb )

# grub-install /dev/sda
# grub-install /dev/sdb
NOT grub-install /dev/sda /dev/sdb
# update-grub2
and, maybe
# update-initramfs

And here is the fdisk -l output:

Disk /dev/sda: 4034 MB, 4034838528 bytes
255 heads, 63 sectors/track, 490 cylinders, total 7880544 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000b4ba7

   Device Boot Start End Blocks Id System
/dev/sda1 63 7871849 3935893+ fd Linux raid autodetect

Disk /dev/sdb: 16.1 GB, 16139354112 bytes
255 heads, 63 sectors/track, 1962 cylinders, total 31522176 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000bd439

   Device Boot Start End Blocks Id System
/dev/sdb1 63 7887914 3943926 fd Linux raid autodetect
/dev/sdb2 7887915 31519529 11815807+ 83 Linux

Disk /dev/md127: 8066 MB, 8066170880 bytes
152 heads, 3 sectors/track, 34548 cylinders, total 15754240 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 524288 bytes / 1048576 bytes
Disk identifier: 0x00065bcb

      Device Boot Start End Blocks Id System
/dev/md127p1 2048 15753215 7875584 83 Linux

P.S. /home is on the /dev/sdb2

ProblemType: Bug
DistroRelease: Ubuntu 11.10
Package: ubiquity 2.7.14
ProcVersionSignature: Ubuntu 3.0.0-7.8-generic 3.0.0
Uname: Linux 3.0.0-7-generic i686
Architecture: i386
Date: Thu Jul 28 15:34:19 2011
ProcEnviron:
 LANG=uk_UA.UTF-8
 SHELL=/bin/bash
SourcePackage: ubiquity
UpgradeStatus: Upgraded to oneiric on 2011-07-28 (0 days ago)