How to mount after raid5 assemble?

Question

I had some raid problems where the raid5 setup in my PR4100 seems to be lost.

I tried everything and ended up manually rebuilding the raid:

mdadm --create --assume-clean --level=raid5 --raid-devices=4 /dev/md1 /dev/sd[abcd]2

Then assemble again

mdadm --assemble /dev/md1 /dev/sda2 /dev/sdb2 /dev/sdc2 /dev/sdd2

after that:

mount /dev/md1 /mnt/HD

But terminal says

mount: /mnt/HD: wrong fs type, bad option, bad superblock on /dev/md1, missing codepage or helper program, or other error.

Any idea?

Also, md1 doesn't get assembled on reboot. The Pr4100 doesn't seem te have a mdadm.config.

EDIT:

Output examine:

root@MyCloudPR4100 dev # mdadm --examine --scan
ARRAY /dev/md/0  metadata=1.2 UUID=2f9fcf63:311fbc6c:2ece20fd:88e3cdda name=MyCloudPR4100:0
ARRAY /dev/md/1  metadata=1.2 UUID=6cdcf758:8fcfb194:3f174806:cc46d6c6 name=MyCloudPR4100:1

The old UUID is stored on the disk in a file called HD_volume_info.xml

<config>
  <volume_info>
    <item>
      <volume>1</volume>
      <web_cmd>10</web_cmd>
      <sdx3_flag>0</sdx3_flag>
      <raid_mode>raid5</raid_mode>
      <file_type>ext4</file_type>
      <size>5577</size>
      <device>sdfsdbsdcsda</device>
      <spare/>
      <mount>/dev/md1</mount>
      <to_be_sync/>
      <used_device>/dev/sdf2 /dev/sdb2 /dev/sdc2 /dev/sda2 </used_device>
      <dev_num>4</dev_num>
      <scsi_mapping>15</scsi_mapping>
      <volume_encrypt>0</volume_encrypt>
      <raid_uuid>UUID=2d967dc8:d8e22fa2:c13058f4:b92320f0</raid_uuid>
      <scsi0_serial>sdf:WD-WCC4M6VAUJSJ</scsi0_serial>
      <scsi1_serial>sdb:WD-WCC4M4KUX9VH</scsi1_serial>
      <scsi2_serial>sdc:WD-WCC4M3TUT1DK</scsi2_serial>
      <scsi3_serial>sda:WD-WCC4M1FUE69R</scsi3_serial>
    </item>
  </volume_info>
</config>

Answer 1

Late to the party here but if you still need help I've worked on data recovery cases like this in the past after a mistaken mdadm --create has been performed.

Briefly stated you can use a brute force method that tries all possible RAID parameter combinations like drive order, chunk size, etc. until the right combination is arrived upon and the data can be accessed.