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List:       linux-raid
Subject:    Re: Impossibly level change request for RAID1
From:       Santiago DIEZ <santiago.diez () caoba ! fr>
Date:       2017-11-21 11:18:03
Message-ID: CAJh8RqWc_jtGQ-Sm-SJLfYcSK75NwfcvOTp09R-7ees2amtYwA () mail ! gmail ! com
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Hi Wol,

This indeed fixed the problem. What I did for the record and for any
newbie reading this post:

# Regrow the RAID1 to 5 devices (this fixed the weird removed messages)
sudo mdadm /dev/md9 --grow --raid-devices=5

# Make 3 disks faulty
sudo mdadm /dev/md9 --fail /dev/sdc9
sudo mdadm /dev/md9 --fail /dev/sdd9
sudo mdadm /dev/md9 --fail /dev/sde9

# Remove 3 disks
sudo mdadm /dev/md9 --remove /dev/sdc9
sudo mdadm /dev/md9 --remove /dev/sdd9
sudo mdadm /dev/md9 --remove /dev/sde9

# Reduce the number of devices in RAID1
sudo mdadm /dev/md9 --grow --raid-devices=2

# Re-attach the 3 disks (they become spare)
sudo mdadm /dev/md9 --add /dev/sdc9
sudo mdadm /dev/md9 --add /dev/sdd9
sudo mdadm /dev/md9 --add /dev/sde9

# Change the level of raid
sudo mdadm /dev/md9 --grow --level=5 --raid-devices=5

# Then wait about 24h for the raid to reshape!

-------------------------
Santiago DIEZ
Quark Systems & CAOBA
23 rue du Buisson Saint-Louis, 75010 Paris
-------------------------

On Wed, Nov 15, 2017 at 6:14 PM, Wols Lists <antlists@youngman.org.uk> wrote:
>
> On 15/11/17 16:52, Santiago DIEZ wrote:
> > Hi,
> >
> > I started by mistake a raid as RAID1 with 5 disks when my desire was
> > to start it as RAID5. Technically, there is no data at all so I could
> > entirely recreate the raid but this is NOT what I want. I'm taking
> > this opportunity as an exercise to change a raid level.
> >
> > The initial state of the raid is:
> > md9 : active raid1 sda9[0] sdb9[1] sdc9[2] sdd9[3] sde9[4]
> >       5846755328 blocks super 1.2 [5/5] [UUUUU]
> >       bitmap: 0/44 pages [0KB], 65536KB chunk
> >
> > # I tried to change the level with:
> > mdadm /dev/md9 --grow --level=5
> > # But got the error :
> > mdadm: Impossibly level change request for RAID1
>
> I'll leave the rest for someone else (or maybe me later :-) but just to
> explain the "impossible level change", you cannot change a mirror with
> more than two active devices. You need to have two active, three spares,
> before it will change.
>
> Cheers,
> Wol
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