Subject: bug#38086: RAID installation script with ‘mdadm’ no longer works

From: Vagrant Cascadian <[email-masked]>
Date: Fri, 17 Jan 2020 14:42:53 -0800

On 2019-11-12, Ludovic Courtès wrote:
> Gábor Boskovits <[email-masked]> skribis:
>
>>> + mdadm --create /dev/md0 --verbose --level=stripe --raid-devices=2
>>> /dev/vdb2 /dev/vdb3
>>> mdadm: chunk size defaults to 512K
>>> mdadm: Defaulting to version 1.2 metadata
>>> [   13.890586] md/raid0:md0: cannot assemble multi-zone RAID0 with
>>> default_layout setting
>>> [   13.894691] md/raid0: please set raid0.default_layout to 1 or 2
>>> [   13.896000] md: pers->run() failed ...
>>> mdadm: RUN_ARRAY failed: Unknown error 524
>>> [   13.901603] md: md0 stopped.
>>> --8<---------------cut here---------------end--------------->8---
>>>
>>> Anyone knows what it takes to “set raid0.default_layout to 1 or 2”?
>>>
>>
>> On kernel 5.3.4 and above the
>> raid0.default_layout=2 kernel boot paramter should be set. We should
>> generate our grub configuration accordingly.

So, this might be sort of a tangent, but I'm wondering why you're
testing raid0 (striping, for performance+capacity at risk of data loss)
instead of raid1 (mirroring, for redundancy, fast reads, slow writes,
half capacity of storage), or another raid level with more disks (raid5,
raid6, raid10). raid1 would be the simplest to switch the code to, since
it uses only two disks.

The issue triggering this bug might be a non-issue on other raid levels
that in my mind might make more sense for rootfs. Or maybe people have
use-casese for rootfs on raid0 that I'm too uncreative to think of? :)

live well,
  vagrant