Preseed RAID10 does not seem to work

Question

I have this config (excerpt) for my preseed

d-i partman-auto/method string raid
d-i partman-auto/disk string /dev/sda /dev/sdb /dev/sdc /dev/sdd

d-i partman-auto/expert_recipe string \
    multiraid:: \
        512 10 512 raid \
            $primary{ } \
            method{ raid } \
        . \
        2000 20 3000 raid \
            method{ raid } \
        . \
        10000 30 4000000 raid \
            method { raid } \
        . \
        1000 40 1000 linux-swap \
            method { swap } \
            format { } \
        .

d-i partman-auto-raid/recipe string \
        10 4 0 ext4 /boot \
            /dev/sda1#/dev/sdb1#/dev/sdc1#/dev/sdd1 \
        . \
        10 4 0 ext4 /   \
            /dev/sda5#/dev/sdb5#/dev/sdc5#/dev/sdd5 \
        . \
        10 4 0 ext4 /var/lib/vz \
            /dev/sda7#/dev/sdb7#/dev/sdc7#/dev/sdd7 \
        .

d-i partman-md/confirm boolean true
d-i partman-md/device_remove_md boolean true

d-i partman/confirm_write_new_label boolean true
d-i partman/choose_partition select finish
d-i partman/confirm boolean true

d-i mdadm/boot_degraded boolean true

With this config I get a "device or resource busy" as soon as it tries to create the second array. Other configs I tried have resulted in things like "Failed to write metadata to /dev/sda2" (when I use primary partitions instead of extended)

Answer 1

I fixed this by manually deleting the Raid devices using mdadm before the partitioning process begins.

From my preseed file:

# This command is run immediately before the partitioner starts. It may be
# useful to apply dynamic partitioner preseeding that depends on the state
# of the disks (which may not be visible when preseed/early_command runs).
d-i partman/early_command string mdadm --stop /dev/md127 && mdadm --remove /dev/md127