Re: mdadm ddf questions

On Tue, 22 Feb 2011 08:41:02 +0100 Albert Pauw [off-list ref] wrote:

  I experimented a bit further, and may have found an error in mdadm.

Again, this was my setup:
- OS Fedora 14 fully updated, running in VirtualBox
- mdadm version 3.1.4, fully updated (as of today) from the git repo
- Five virtual disks, 1 GB each, to use

I created two raid sets out of one ddf container:

mdadm -C /dev/md127 -l container -e ddf -n 5 /dev/sd[b-f]
mdadm -C /dev/md1 -l 1 -n 2 /dev/md127
mdadm -C /dev/md2 -l 2 -n 3 /dev/md127

Disks sdb and sdc were used for the RAID 1 set, disks sdd, sde, sdf were 
used for the RAID 5 set.
All were fine and the command mdadm -E /dev/md127 showed all disks 
active/Online

Now I failed one of the disks of md1:

mdadm -f /dev/md1 /dev/sdb

Indeed, looking at /proc/mdstat I saw the disk marked failed [F] before 
it was automatically removed within a second (a bit weird).

Now comes the weirdest part, mdadm -E /dev/md127 did show one disk as 
"active/Online, Failed" but this was disk sdd
which is part of the other RAID set!

Yes .. that is weird.  I can reproduce this easily.
I had a look through the code and it looks right so there must be something
subtle...  I'll look more closely next wee when I'll have more time.

When I removed the correct disk, which can only be done from the container:

mdadm -r /dev/md127 /dev/sdb

the command mdadm -E /dev/md127 showed the 5 disks, the entry for sdb 
didn't had a device but was still
"active/Online" and sdd was marked Failed:

Physical Disks : 5
         Number       RefNo             Size            Device           
Type/State
                 0       d8a4179c    
1015808K                             active/Online
                 1       5d58f191    1015808K     /dev/sdc           
active/Online
                 2       267b2f97    1015808K     /dev/sdd           
active/Online. Failed
                 3       3e34307b   1015808K     /dev/sde           
active/Online
                 4       6a4fc28f     1015808K     /dev/sdf           
active/Online

When I try to mark sdd as failed, mdadm tells me that it did it, but 
/proc/mdstat doesn't show the disk as failed,
everything is still running. I also am not able to remove it, as it is 
in use (obviously).

So it looks like there are some errors in here.

Thanks!

NeilBrown