Re: regression: drive was detected as raid member due to metadata on partition

[Li Nan <linan666@huaweicloud.com>]

Hi, Köhler

在 2024/4/9 7:31, Sven Köhler 写道:
> Hi,
> 
> I was shocked to find that upon reboot, my Linux machine was detecting 
> /dev/sd[abcd] as members of a raid array. It would assign those members to  
> /dev/md4. It would not run the raid arrays /dev/mdX with members 
> /dev/sda[abcd]X for X=1,2,3,4 as it usually did for the past couple of years.
> 
> My server was probably a unicorn in the sense that it used metadata version 
> 0.90. This version of software RAID metadata is stored at the _end_ of a 
> partition. In my case, /dev/sda4 would be the last partition on drive 
> /dev/sda. I confirmed with mdadm --examine that metadata with the identical 
> UUID would be found on both /dev/sda4 and /dev/sda.
> 

I am trying to reproduce it, but after reboot, md0 started with members
/dev/sd[bc]2 correctly. And mdadm will waring if assemble by 'mdadm -A'.

   # mdadm -CR /dev/md0 -l1 -n2 /dev/sd[bc]2 --metadata=0.9
   # mdadm -S --scan
   # mdadm -A --scan
   mdadm: WARNING /dev/sde2 and /dev/sde appear to have very similar 
superblocks.
         If they are really different, please --zero the superblock on one
         If they are the same or overlap, please remove one from the
         DEVICE list in mdadm.conf.
   mdadm: No arrays found in config file or automatically

Can you tell me how you create and config the RAID?

> Here's what I think went wrong: I believe either the kernel or mdadm 
> (likely the latter) was seeing the metadata at the end of /dev/sda and 
> ignored the fact that the location of the metadata was actually owned by a 
> partition (namely /dev/sda4). The same happened for /dev/sd[bcd] and thus I 
> ended up with /dev/md4 being started with members /dev/sda[abcd] instead of 
> members /dev/sda[abcd]4.
> 
> This behavior started recently. I saw in the logs that I had updated mdadm 
> but also the Linux kernel. mdadm and an appropriate mdadm.conf is part of 
> my initcpio. My mdadm.conf lists the arrays with their metadata version and 
> their UUID.
> 
> Starting a RAID array with members /dev/sda[abcd] somehow removed the 
> partitions of the drives. The partition table would still be present, but 
> the partitions would disappear from /dev. So /dev/sda[abcd]1-3 were not 
> visible anymore and thus /dev/md1-3 would not be started.
> 
> I strongly believe that mdadm should ignore any metadata - regardless of 
> the version - that is at a location owned by any of the partitions. While 
> I'm not 100% sure how to implement that, the following might also work: 
> first scan the partitions for metadata, then ignore if the parent device 
> has metadata with a UUID previously found.
> 
> 
> I did the right thing and converted my RAID arrays to metadata 1.2, but I'd 
> like to save other from the adrenaline shock.
> 
> 
> 
> Kind Regards,
>    Sven
> 
> .

-- 
Thanks,
Nan