With the following configuration, any attempt to access /dev/md1 will lock the process in D (disk sleep) state: raiddev /dev/md0 raid-level 1 nr-raid-disks 2 nr-spare-disks 0 persistent-superblock 1 chunk-size 64 device /dev/hda5 raid-disk 0 device /dev/hda6 raid-disk 1 raiddev /dev/md1 raid-level linear nr-raid-disks 2 chunk-size 4 persistent-superblock 0 device /dev/md0 raid-disk 0 device /dev/hda7 raid-disk 1 On the other hand, the following configuration works just fine: raiddev /dev/md0 raid-level 1 nr-raid-disks 2 nr-spare-disks 0 persistent-superblock 1 chunk-size 64 device /dev/hda5 raid-disk 0 device /dev/hda6 raid-disk 1 raiddev /dev/md1 raid-level linear nr-raid-disks 2 chunk-size 4 persistent-superblock 0 device /dev/hda8 raid-disk 0 device /dev/hda7 raid-disk 1