Grub won't boot from GPT RAID (gave up waiting for root dev)

[Uriel32]

I'm having problems with booting a Debian 8 system on which I migrated the root partition from a single hard drive to a RAID1 (mdraid).

On every boot I get the following grub error:

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Gave up waiting for root device. Common problems:
 - Boot args (cat /proc/cmdline)
   - Check rootdelay= (did the system wait long enough?)
   - Check root= (did the system wait for the right device?)
 - Missing modules (cat /proc/modules; ls /dev)
ALERT! /dev/disk/by-uuid/2ab18cb4-a23d-4e5c-b37d-cbd3077b878c does not exist.
Dropping to a shell!
modprobe: module ehci-orion not found in modules.dep

(initramfs)

/dev/md0 is not started, so it can't find the root partition:

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(initramfs) ls /dev/md*
ls: /dev/md*: No such file or directory
(initramfs)

I can however start the raid manually just fine:

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(initramfs) mdadm --assemble --scan
mdadm: /dev/md0 has been started with 2 drives.
(initramfs) ls /dev/md*
/dev/md0

The System will only boot if I manually create the directory /dev/disk/by-uuid and link md0:
(shouldn't at least /dev/disk/by-uuid already exist?)

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(initramfs) mkdir /dev/disk/by-uuid
(initramfs) ln -s /dev/md0 /dev/disk/by-uuid/2ab18cb4-a23d-4e5c-b37d-cbd3077b878c

I hope someone can help me figure out why grub doesn't start the md device by itself. I searched the internet and tried about everything I could find but no luck. I'm really lost right now.

Additional info:

(I want to boot via BIOS-legacy, not UEFI)

The only two connected hard drives (SSD!) are formated with a GPT partition table and the following partitions:
(grub-pc needs the first partition to boot from GPT drives)

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1      1049kB  2097kB  1049kB                     bios_grub
2      2150MB  12,9GB  10,7GB  ext4               raid

The Raid1 (v0.90 metadata) is formated directly as ext4.

Through a live system chroot I installed grub-pc to /dev/sda and /dev/sdb, changed my fstab, ran update-grub and update-initramfs -u -k all.
blkid:

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/dev/sda2: UUID="b59d3baf-346b-568d-03a2-8b26060640c5" TYPE="linux_raid_member" PARTUUID="0609ba5b-9065-41f8-80ed-6832e3236ec9"
/dev/sdb2: UUID="b59d3baf-346b-568d-03a2-8b26060640c5" TYPE="linux_raid_member" PARTUUID="24ee1040-02dd-4867-b4da-5be11d59bdcd"
/dev/md0: UUID="2ab18cb4-a23d-4e5c-b37d-cbd3077b878c" TYPE="ext4"
/dev/sda1: PARTUUID="df5161cf-b5b3-422c-9ed2-90a7750ac265"
/dev/sdb1: PARTUUID="7d20b55b-ba50-4187-b05e-ae1f18b21de3"

mdadm.conf contains (only!) the content from mdadm --detail --scan:

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ARRAY /dev/md0 metadata=0.90 UUID=b59d3baf:346b568d:03a28b26:060640c5

Here is an excerpt from my /boot/grub/grub.cfg:

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load_video
insmod gzio
if [ x$grub_platform = xxen ]; then insmod xzio; insmod lzopio; fi
insmod part_gpt
insmod part_gpt
insmod diskfilter
insmod mdraid09
insmod ext2
set root='mduuid/b59d3baf346b568d03a28b26060640c5'
if [ x$feature_platform_search_hint = xy ]; then
  search --no-floppy --fs-uuid --set=root --hint='mduuid/b59d3baf346b568d03a28b26060640c5'  2ab18cb4-a23d-4e5c-b37d-cbd3077b878c
else
  search --no-floppy --fs-uuid --set=root 2ab18cb4-a23d-4e5c-b37d-cbd3077b878c
fi
echo        'Linux 3.16.0-4-amd64 wird geladen …'
linux       /boot/vmlinuz-3.16.0-4-amd64 root=UUID=2ab18cb4-a23d-4e5c-b37d-cbd3077b878c ro  rootdelay=20
echo        'Initiale Ramdisk wird geladen …'
initrd      /boot/initrd.img-3.16.0-4-amd64

I can reproduce this in a virtual machine:

• - Create GPT partition table on disk
  - Install Debian to disk
  - Create two slightly larger virtual disks with RAID on them
  - Copy partitions to RAID
  - Install grub on both RAID members
  - Update initramfs