Re: Why does md3 persist after deleting and recreating the partitions?

[Neil Brown <neilb@suse.de>]

On Thu, 30 Dec 2010 16:17:51 -0800 Mark Knecht <markknecht@gmail.com> wrote:

> On Thu, Dec 30, 2010 at 4:16 PM, Mathias Burén <mathias.buren@gmail.com> wrote:
> > On 31 December 2010 00:14, Mark Knecht <markknecht@gmail.com> wrote:
> >> On Thu, Dec 30, 2010 at 4:12 PM, Mathias Burén <mathias.buren@gmail.com> wrote:
> >>> On 31 December 2010 00:10, Mark Knecht <markknecht@gmail.com> wrote:
> >>>> Hi,
> >>>>   What am I forgetting to do? I had a RAID1 using sd{a,b,c}3. I
> >>>> stopped md3, removed the md3 line in /etc/mdadm.conf, deleted the
> >>>> partitions using fdisk, and then created 5 new partitions using
> >>>> sd{a,b,c,d,e}3 to get ready to do a 5 disk RAID6. The new partitions
> >>>> are the same size as the old ones and located at the same sector
> >>>> addresses.
> >>>>
> >>>>   After rebooting, but before creating the new RAID6, I still see md3:
> >>>>
> >>>> mark@c2stable ~ $ cat /proc/mdstat
> >>>> Personalities : [linear] [raid0] [raid1] [raid10] [raid6] [raid5] [raid4]
> >>>> md6 : active raid1 sdb6[1] sdc6[2] sda6[0]
> >>>>      247416933 blocks super 1.1 [3/3] [UUU]
> >>>>
> >>>> md3 : active raid1 sdc3[2] sdb3[1] sda3[0]
> >>>>      52436096 blocks [3/3] [UUU]
> >>>>
> >>>> md5 : active raid1 sdc5[2] sdb5[1] sda5[0]
> >>>>      52436032 blocks [3/3] [UUU]
> >>>>
> >>>> unused devices: <none>
> >>>> mark@c2stable ~ $
> >>>>
> >>>>
> >>>>   What am I doing wrong or forgetting? I would like md3 to be totally
> >>>> gone before I create a new md3 in it's place.
> >>>>
> >>>> Thanks,
> >>>> Mark
> >>>> --
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> >>>>
> >>>
> >>> Erase the superblocks? Recreating partitions doesn't (usually) affect
> >>> the data on the HDDs.
> >>>
> >>> // M
> >>>
> >>
> >> Is erasing the superblocks a mdadm operation? I've not heard of that one before.
> >>
> >> Thanks,
> >> Mark
> >>
> >
> > Yes, see mdadm --misc. Like:
> >
> > mdadm --zero-superblock <device>
> >
> > // M
> >
> 
> Yes, just found that.
> 
> Can I still use /dev/md3 safely even though it's no longer in
> mdadm.conf? I suspect I can?

That sentence doesn't make much sense to me, so I suspect some misunderstand
is going on.  So to be explicit:

  Use
    mdadm --zero-superblock /dev/sdc3 /dev/sdb3 /dev/sda3

 to remove  from those devices any record that they are part of any md array.

Does that clarify thing sufficienty?

NeilBrown

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