Re: Requesting replace mode for changing a disk

[Neil Brown <neilb@suse.de>]

On Wednesday May 13, goswin-v-b@web.de wrote:
> > OK, basically the same question.  How does one disassemble the RAID1 array
> > without wiping the data on the new drive?
> 
> I think he ment this:
> 
> mdadm --stop /dev/md0
> mdadm --build /dev/md9 --chunk=64k --level=1 --raid-devices=2 /dev/suspect /dev/new
> mdadm --assemble /dev/md0 /dev/md9 /dev/other ...

or better still:

  mdadm --grow /dev/md0 --bitmap internal
  mdadm /dev/md0 --fail /dev/suspect --remove /dev/suspect
  mdadm --build /dev/md9 --level 1 --raid-devices 2 /dev/suspect missing
  mdadm /dev/md0 --add /dev/md9
  mdadm /dev/md9 --add /dev/new

no down time at all.  The bitmap ensures that /dev/md9 will be
recovered almost immediately once it is added back in to the array.

The one problem with this approach is that if there is a read error on
/dev/suspect while data is being copied to /dev/new, you lose.

Hence the requested functionality which I do hope to implement for
raid456 and raid10 (it adds no value to raid1).
Maybe by the end of this year... it is on the roadmap.

NeilBrown