On Fri May 08, 2015 at 11:18:44AM +0200, Hans Kraus wrote:

Hi,

I have a Raid 1 with 3 drives, the following layout (the internal
bitmap is already removed):
-----------------------------------------------------------------
md20 : active raid1 sdj1[2] sdi1[1] sdn1[0]
       732442432 blocks super 1.2 [3/3] [UUU]
-----------------------------------------------------------------
I tried to change it to Raid 5, but I'm getting aways an error.
-----------------------------------------------------------------
mdadm --grow /dev/md20 --level=5 --raid-devices=3 -c 32 \
   --backup-file=/home/kraush/work/raidLevelChange

Impossibly level change request for RAID1
-----------------------------------------------------------------
I tried it with various permutations (+/- raid-devices, c, ...).

Is something in my command wrong or is the level change not
possible?
This is on Debian 7, mdadm - v3.3-65-g2167de7 - 11th March 2014

I think you'll need one of the disks to be spare first. Try reducing the
RAID1 to a 2-disk plus spare configuration, then rerunning the grow.
Alternately you'd need to add a new disk as a spare first, then grow to
a 4 disk RAID5.

HTH,
    Robin
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