Re: Converting RAID1 to RAID5

[NeilBrown <neilb@suse.de>]

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On Thu, 15 Sep 2011 19:50:08 -0400 Alex <mysqlstudent@gmail.com> wrote:

> Hi,
> 
> Last week you were helping me with trying to convert a RAID1 volume to
> RAID5. I've put together a server to test, and have made some
> progress, but have a few questions.
> 
> >  then try some things. e.g.
> >
> >  mdadm /dev/md0 --add /dev/loop2
> >  mdadm --grow /dev/md0 --level=5 --raid-devices=3
> >
> >  Try failing a device during the reshape.  Check if the data is still OK.
> >  Try it as two separate steps and see if it makes a difference.
> 
> I partitioned a third disk in the same way as the other two, and
> successfully added them to their existing respective volumes as
> spares.
> 
> I was able to grow md0, which is mounted on /boot, and it resynced it
> and successfully converted it to RAID5.
> 
> When I try to grow the other two partitions (/ and /home), it fails
> with device busy:
> 
> # mdadm --grow /dev/md2 --level=5 --raid-devices=3
> mdadm: level of /dev/md2 changed to raid5
> mdadm: Need to backup 128K of critical section..
> mdadm: Cannot set device shape for /dev/md2: Device or resource busy
>        Bitmap must be removed before shape can be changed
         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> mdadm: aborting level change
> 
> # cat /proc/mdstat
> Personalities : [raid1] [raid6] [raid5] [raid4]
> md2 : active raid1 sdc3[2](S) sda3[0] sdb3[1]
>       186366908 blocks super 1.1 [2/2] [UU]
>       bitmap: 1/2 pages [4KB], 65536KB chunk
> 
> md1 : active raid1 sdc2[2](S) sda2[0] sdb2[1]
>       51198908 blocks super 1.1 [2/2] [UU]
>       bitmap: 1/1 pages [4KB], 65536KB chunk

You need to remove those bitmaps first.  Put them back after the reshape
completes.
(mdadm --grow --bitmap=none ; mdadm --grow --bitmap=internal)

> 
> md0 : active raid5 sdc1[2] sda1[0] sdb1[1]
>       1023976 blocks super 1.0 level 5, 4k chunk, algorithm 2 [3/3] [UUU]
> 
> unused devices: <none>
> 
> /dev/md2 (/home) isn't mounted.
> 
> When the conversion to RAID5 is complete, how can I regenerate the
> mdadm.conf to properly reflect the change?

I would use an editor.
The output of "mdadm -Ds" could be a helpful guide.

NeilBrown

> 
> Thanks,
> Alex


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