On 2018-09-03 08:48, Guoqing Jiang wrote: > On 08/31/2018 05:18 PM, Guoqing Jiang wrote: >> On 08/30/2018 10:32 AM, Niklas Hambüchen wrote: >>> Is it expected that raid1 turns into raid0 in this way when during a reboot an expected device is not present (e.g. because it is unplugged or was replaced)? >>> If yes, what is the idea behind that, and why doesn't it go into the normal degraded mode instead? >>> Is it possible to achieve that? I had hoped that I would be able to continue booting into a degraded system if a disk fails during a reboot (and then be notified of the degradation by mdadm as usual), but this isn't the case if an array comes back as raid0 and inactive after reboot. >>> Finally, if these topics are already explained somewhere, where can I read more about it? >> >> Maybe we need to call do_md_run when assembling an array, need to investigate it. > > It doesn't work, actually the array can be activated by "echo active > /sys/block/md0/md/array_state". Thank you, this echo worked! I just confirmed it on another machine. It immediately brings the array back from the wrong "Raid Level : raid0" into the correct "raid1". I also noticed that `mdadm --run /dev/md0` has the same effect. But `mdadm --run --readonly /dev/md0` didn't, it says "/dev/md0 does not appear to be active".) So remaining question is: Why does the device appear as raid0 at all? I would expect it to come back from reboot as a degraded raid1, because that's what it is (and mdadm seems to think so too as soon as you activate it).
