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I have an Ubuntu 16.06 system where / on an SSD primary partition and /home with md RAID0 on four SSD devices. The file /etc/mdadm/mdadm.conf is automatically generated by mkconf and contains no devices nor arrays. I have UUID=<uuid for fs> /home ext4 defaults in /etc/fstab and that is enough to assemble the RAID. The system boots fine, correctly assembles the RAID and mounts it as expected. However, after upgrading packages update-initramfs always emits a warning

W: mdadm: /etc/mdadm/mdadm.conf defines no arrays.

How can I keep using the fully automatic RAID assembly with only /etc/fstab containing the file system UUID for /home and avoid the warning message from update-initramfs?

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Update your initramfs as outlined in the manual by copying the mdadm.conf into /etc/update-initramfs/etc folder (not tested, it may have to be an mdadm subfolder).

  • I don't agree with this solution. After digging around in the filesystem I found that warning is emitted by /usr/share/initramfs-tools/hooks/mdadm. There's a simple grep -q '^ARRAY' against current mdadm configuration and warning message will be emitted if the above regexp does not match at least once. The system works fine with that so I opted to change warn to info in that file and just forget about the issue. – Mikko Rantalainen Oct 10 '16 at 12:50
  • That would work as well. – jas- Oct 10 '16 at 13:26

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