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

[Roy Sigurd Karlsbakk <roy@karlsbakk.net>]

> In my continuing goal to remove the bad blocks log from any of my
> arrays and not have one on any new arrays I create, I wrote this
> article:
> 
>    https://strugglers.net/~andy/blog/2020/09/13/debian-installer-mdadm-configuration-and-the-bad-blocks-controversy
> 
> Shortly afterwards someone on Hacker News¹ said that it is possible
> to remove the BBL by failing and re-adding devices, like so:
> 
> # mdadm /dev/md127 --fail /dev/sda --remove /dev/sda --re-add /dev/sda
> --update=no-bbl
> 
> I tried that on Ubuntu 18.04:
> 
> $ mdadm --version
> mdadm - v4.1-rc1 - 2018-03-22
> $ sudo mdadm --fail /dev/md0 /dev/sdb1 --remove /dev/sdb1 --re-add /dev/sdb1
> --update=no-bbl
> mdadm: set /dev/sdb1 faulty in /dev/md0
> mdadm: hot removed /dev/sdb1 from /dev/md0
> mdadm: --re-add for /dev/sdb1 to /dev/md0 is not possible
> $ sudo mdadm --add /dev/md0 /dev/sdb1 --update=no-bbl
> mdadm: --update in Manage mode only allowed with --re-add.
> $ sudo mdadm --add /dev/md0 /dev/sdb1
> mdadm: added /dev/sdb1
> $ sudo mdadm --examine-badblocks /dev/sdb1
> Bad-blocks list is empty in /dev/sdb1
> 
> I tried it on Debian buster:
> 
> $ mdadm --version
> mdadm - v4.1 - 2018-10-01
> $ sudo mdadm --fail /dev/md6 /dev/sdb1 --remove /dev/sdb1 --re-add /dev/sdb1
> --update=no-bbl
> mdadm: set /dev/sdb1 faulty in /dev/md6
> mdadm: hot removed /dev/sdb1 from /dev/md6
> 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.

I've tried this as well, and ran

mddev=/dev/md0
diskdev=/dev/sdm

mdadm --fail $mddev $diskdev
mdadm --remove $mddev $diskdev
mdadm --re-add $mddev $diskdev

All returned ok, but sdm was listed as a slave, thus not active anymore. After this, a new --remove and --re-add didn't work, so it'll take some hours to --add it again (yet another time).

It would be very nice if someone at linux-raid could prioritise this rather obvious bug in the bbl code, where the bbl keeps replicating itself over and over, regardless of any actual failures on the disks. IMHO the whole BBL should be scrapped, as mentioned earlier, since it really has no function. Mapping out bad sectors is for the drive to decide and if it can't handle it, it should be kicked out of the array.

Vennlig hilsen

roy
-- 
Roy Sigurd Karlsbakk
(+47) 98013356
http://blogg.karlsbakk.net/
GPG Public key: http://karlsbakk.net/roysigurdkarlsbakk.pubkey.txt
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