Re: [BUG?] Grow on raid0 causes a level change to raid4 on metadata v1.2

Re: [BUG?] Grow on raid0 causes a level change to raid4 on metadata v1.2

[NeilBrown]

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On Fri, 23 Nov 2012 14:06:09 +0000 "Tomczak, Marcin"
<marcin.tomczak@intel.com> wrote:

> Hi. There is a problem when I try to resize raid0 by adding disk to raid 
> volume. I have checked the problem on mdadm v3.2.3 and on a code from 
> neil_master branch.
> 
> OS: Red Hat 6.3 GA
> reproduction: always
> system disk: sda
> other disks: sdb, sdc, sdd
> 
> 
> I. mdadm version: v3.2.3
> 
> # mdadm -CR /dev/md/vol metadata=1.2 -l 0 --size=4G -n 2 /dev/sdb /dev/sdc
> # mdadm -G /dev/md/vol -n 3 --add /dev/sdd
> mdadm: /dev/md/vol: could not set level to raid4
> 
> 
> II. mdadm version: branch neil_master
> 
> SHA1 ID: 30d48159710996be7770bfbfbddc826317b561aa
> Monitor: don't complain about non-monitorable arrays in mdadm.conf
> Author: NeilBrown <neilb@suse.de>  2012-10-24 04:09:09
> Committer: NeilBrown <neilb@suse.de>  2012-10-24 04:09:09
> 
> # mdadm -CR /dev/md127 --metadata=1.2 -l 0 --size=15G -n 2 /dev/sdb /dev/sdc

--size isn't honoured for RAID0 (or Linear).  I should probably do something
about that - generate a warning at least.

> # mdadm -G /dev/md127 -n 3 --add /dev/sdd
> mdadm: level of /dev/md127 changed to raid4
> mdadm: added /dev/sdd
> mdadm: this change will reduce the size of the array.
>        use --grow --array-size first to truncate array.
>        e.g. mdadm --grow /dev/md127 --array-size 47185920

This happens because the metadata has a size recorded in it, but it is being
ignored, which results in confusions.


> # cat /proc/mdstat
> Personalities : [raid0] [raid6] [raid5] [raid4]
> md127 : active raid4 sdd[3] sdc[1] sdb[0]
>       78107648 blocks super 1.2 level 4, 512k chunk, algorithm 5 [3/3] [UUU]
> 
> 
> What do you think about this mdadm behaviour?

Not ideal, but not a big problem if you avoid trying to set --size for RAID0.

NeilBrown


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