Re: Weirdness with DDF arrays (mdadm 3.3)

[Martin Wilck <mwilck@arcor.de>]

Hi Francis, hi Neil,

> Still testing MD arrays using DDF metadata and find another possible issues :)
> 
> I'm creating a new DDF array containing 2 disks. After that
> /proc/mdstat looks correct:
> 
> # cat /proc/mdstat
> Personalities : [raid1]
> md124 : active raid1 loop0[1] loop1[0]
>       84416 blocks super external:/md125/0 [2/2] [UU]
> 
> md125 : inactive loop1[1](S) loop0[0](S)
>       65536 blocks super external:ddf
> 
> Now I'm stopping the array and restart it by incrementaly adding the 2 disks:
> # mdadm --stop /dev/md124
> # mdadm --stop /dev/md125
> # mdadm -IRs /dev/loop0

This is wrong, because -IRs "wills can the mapfile for arrays that are
being incrementally assembled snd will try to start any that are not
already started".

mdadm -IRs will first add /dev/loop0, then see that there is an
incomplete array, and start it.

> # mdadm -IRs /dev/loop1

Now you add /dev/loop1, but as the array is already started, it will be
added as a spare. That's what you see below.

However, there is room for improvement here. The array hasn't been
written to, so even if it is started, it should be possible to re-add
the second disk cleanly.

Looking into that.

Martin


> # cat /proc/mdstat
> Personalities : [raid1]
> md124 : active (auto-read-only) raid1 loop1[2] loop0[0]
>       84416 blocks super external:/md125/0 [2/1] [_U]
> 
> md125 : inactive loop1[1](S) loop0[0](S)
>       65536 blocks super external:ddf
> 
> Parsing mdstat content tells me disk "loop1" have a role number equal
> to 2 which is greater than 1 indicating that "loop1" is a spare disk
> and the "[_U]" below indicates "loop1" is down".
> 
> Why is "loop1" down now ?
> 
> I decided to still use the md device by creating a new partition on it:
> # fdisk /dev/md124
> ...
> Calling ioctl() to re-read partition table.
> Syncing disks.
> 
> Now inspecting /proc/mdstat:
> 
> # cat /proc/mdstat
> Personalities : [raid1]
> md124 : active raid1 loop1[2] loop0[0]
>       84416 blocks super external:/md125/0 [2/2] [UU]
> 
> md125 : inactive loop1[1](S) loop0[0](S)
>       65536 blocks super external:ddf
> 
> which looks even weirder: "loop1[2]" indicates that the disk is a
> spare one whereas "[UU]" tells me the opposite.
> 
> Could you tell me if I'm wrong in my interpretation or what's going wrong ?
> 
> Thanks