Problem converting from raid5 to raid6

Problem converting from raid5 to raid6

[Shane W]

Hello all,

I am trying to convert a 5 disk raid5 array to a 6 disk
raid6 but am having no luck. I first added the 6th disk as
a spare then
mdadm --grow /dev/md3 --level 6
mdadm level of /dev/md3 changed to raid6
mdadm: /dev/md3: Something wrong - reshape aborted
mdadm: aborting level change

dmesg doesn't show an error and neither does mdadm beyond
"something wrong". Is this supported?

mdadm 3.1.1 Linux 2.6.32.8 x86_64.

Thanks,
Shane

Re: Problem converting from raid5 to raid6

[Michael Evans]

On Sat, Mar 20, 2010 at 8:01 PM, Shane W <shane-kernel@csy.ca> wrote:
> Hello all,
>
> I am trying to convert a 5 disk raid5 array to a 6 disk
> raid6 but am having no luck. I first added the 6th disk as
> a spare then
> mdadm --grow /dev/md3 --level 6
> mdadm level of /dev/md3 changed to raid6
> mdadm: /dev/md3: Something wrong - reshape aborted
> mdadm: aborting level change
>
> dmesg doesn't show an error and neither does mdadm beyond
> "something wrong". Is this supported?
>
> mdadm 3.1.1 Linux 2.6.32.8 x86_64.
>
> Thanks,
> Shane
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It should be supported, but you probably need to specify a temporary
file ON ANOTHER DEVICE where the 'critical section' can be backed up
to and restored in case the reshape fails.  I forget what the exact
syntax is, but man mdadm will inform you.
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Re: Problem converting from raid5 to raid6

[Kristleifur Daðason]

On Sun, Mar 21, 2010 at 10:28 AM, Michael Evans <mjevans1983@gmail.com> wrote:
> On Sat, Mar 20, 2010 at 8:01 PM, Shane W <shane-kernel@csy.ca> wrote:
>> Hello all,
>>
>> I am trying to convert a 5 disk raid5 array to a 6 disk
>> raid6 but am having no luck. I first added the 6th disk as
>> a spare then
>> mdadm --grow /dev/md3 --level 6
>> mdadm level of /dev/md3 changed to raid6
>> mdadm: /dev/md3: Something wrong - reshape aborted
>> mdadm: aborting level change
>>
>> dmesg doesn't show an error and neither does mdadm beyond
>> "something wrong". Is this supported?
>>
>> mdadm 3.1.1 Linux 2.6.32.8 x86_64.
>>
>> Thanks,
>> Shane

+1 on the critical section backup

And some bonus info: If you have a write-intent bitmap on the RAID5
array, you may have to get the bitmap out of the way of the reshape.
This one got me for a while. (I'm not sure about all cases, but I
believe you have to turn the bitmap off. I had an _internal_ bitmap,
turned it off, and only then my reshape kicked into gear. Remember to
turn it back on :) )

Good luck!

-- Kristleifur

Re: Problem converting from raid5 to raid6

[Neil Brown]

On Sat, 20 Mar 2010 20:01:07 -0700
Shane W <shane-kernel@csy.ca> wrote:

> Hello all,
> 
> I am trying to convert a 5 disk raid5 array to a 6 disk
> raid6 but am having no luck. I first added the 6th disk as
> a spare then
> mdadm --grow /dev/md3 --level 6
> mdadm level of /dev/md3 changed to raid6
> mdadm: /dev/md3: Something wrong - reshape aborted
> mdadm: aborting level change
> 
> dmesg doesn't show an error and neither does mdadm beyond
> "something wrong". Is this supported?
> 
> mdadm 3.1.1 Linux 2.6.32.8 x86_64.
>


That shouldn't happen.... How big is your array?  How many devices?
Chunksize? etc.

Maybe just the output of
  mdadm -D /dev/md3

would do.

NeilBrown