Creating volume in IMSM container

Creating volume in IMSM container

[Ian Pilcher]

I am trying to create an IMSM container and volume in a KVM virtual
machine (so that I can create a reproducer for a Fedora problem that
seems to only/mostly affect IMSM RAID).  I've  managed to create a
container with the following command:

   IMSM_NO_PLATFORM=1 mdadm --create --verbose /dev/md/imsm \
       /dev/vd{a,b} --raid-devices 2 --metadata=imsm

/proc/mdstat now contains:

   Personalities: [raid0] [raid1] [raid6] [raid5] [raid4] [raid10] ...
   md127 : inactive vdb[1](S) vda[0](S)
         2210 blocks super external:imsm

I haven't, however, been able to create a volume within the container:

   # IMSM_NO_PLATFORM=1 mdadm --create --verbose /dev/md/vol0 \
        /dev/md/imsm --raid-devices 2 --level 1 --metadata=imsm
   mdmon: not enough devices with space to create array.

   # IMSM_NO_PLATFORM=1 mdadm --create --verbose /dev/md/vol0 \
        /dev/vd{a,b} --raid-devices 2 --level 1 --metadata=imsm
   mdadm: /dev/vda appears to be part of a raid array:
          level=container devices=0 ctime=Thu Jan  1 00:00:00 1970
   mdmon: /dev/vdb is not in the same imsm set
   mdadm: /dev/vdb is not suitable for this array.
   mdadm: create aborted

Am I doing something wrong, or is this simply not possible?

-- 
========================================================================
Ian Pilcher                                         arequipeno@gmail.com
-------- "I grew up before Mark Zuckerberg invented friendship" --------
========================================================================

Re: Creating volume in IMSM container

[NeilBrown]

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On Tue, 07 Apr 2015 10:29:02 -0500 Ian Pilcher <arequipeno@gmail.com> wrote:

> I am trying to create an IMSM container and volume in a KVM virtual
> machine (so that I can create a reproducer for a Fedora problem that
> seems to only/mostly affect IMSM RAID).  I've  managed to create a
> container with the following command:
> 
>    IMSM_NO_PLATFORM=1 mdadm --create --verbose /dev/md/imsm \
>        /dev/vd{a,b} --raid-devices 2 --metadata=imsm
> 
> /proc/mdstat now contains:
> 
>    Personalities: [raid0] [raid1] [raid6] [raid5] [raid4] [raid10] ...
>    md127 : inactive vdb[1](S) vda[0](S)
>          2210 blocks super external:imsm

2210 blocks is tiny.
I think each device needs at least 6306 sectors for IMSM.
I suggest going for at least 20,000.

> 
> I haven't, however, been able to create a volume within the container:
> 
>    # IMSM_NO_PLATFORM=1 mdadm --create --verbose /dev/md/vol0 \
>         /dev/md/imsm --raid-devices 2 --level 1 --metadata=imsm
>    mdmon: not enough devices with space to create array.

This should  work once you have devices with enough space.

> 
>    # IMSM_NO_PLATFORM=1 mdadm --create --verbose /dev/md/vol0 \
>         /dev/vd{a,b} --raid-devices 2 --level 1 --metadata=imsm
>    mdadm: /dev/vda appears to be part of a raid array:
>           level=container devices=0 ctime=Thu Jan  1 00:00:00 1970
>    mdmon: /dev/vdb is not in the same imsm set
>    mdadm: /dev/vdb is not suitable for this array.
>    mdadm: create aborted
> 

This looks like a bug.  What version of mdadm.

NeilBrown


> Am I doing something wrong, or is this simply not possible?
> 


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