The the default configuration under ArchLinux and DEVICE partitions in mdadm.conf, mdadm and the mdadm mkinitcpio hook fail to load the raid10 kernel module automatically, and as a result raid10 arrays fail to load on boot in Arch. My temporary workaround is to include the raid10 kernel module in the mkinitcpio.conf MODULES= list, it could also be included in /etc/modules-load.d/*.conf, but this should not be necessary, and is currently not necessary for raid1 arrays. I do not think this is an upstream problem since my LFS and Gentoo boxes do load the correct (raid10) kernel module without any specific configuration to do so. Has anyone else replicated this behavior? Suggestions: - Preferred: Make the initcpio hook/mdadm udev rules/whatever loads raid1.ko normally also detect raid10 (and raid5, raid6, ...) arrays properly. - Alternatively: Add a section to the SW RAID wiki page describing how to make the module load persist on boot (https://wiki.archlinux.org/index.php/Software_RAID_and_LVM#Load_kernel_modul...) Ido