Re: "--re-add for /dev/sdb1 to /dev/md0 is not possible"

[Andy Smith <andy@strugglers.net>]

On Tue, Sep 15, 2020 at 10:27:36AM +0000, Andy Smith wrote:
> mdadm: --re-add for /dev/sdb1 to /dev/md6 is not possible
> 
> So, is that supposed to work and if so, why doesn't it work for me?
> 
> In both cases these are simple two device RAID-1 metadata version
> 1.2 arrays. Neither has bitmaps.

The lack of bitmaps was why I couldn't use --re-add. I was testing
with small arrays that didn't get a bitmap by default. As mentioned
on the wiki, a bitmap can be added like:

# mdadm --grow --bitmap=internal /dev/mdX

So, as pointed out to me by Jakub Wilk, it is possible to remove the
bad blocks log on a running array by failing and re-adding each
device in turn, as long as you are willing to experience lower / no
redundancy while it rebuilds.

# mdadm --fail /dev/md0 /dev/sdb1 \
        --remove /dev/sdb1 \
        --re-add /dev/sdb1 \
        --update=no-bbl

Cheers,
Andy