Re: RAID5 -> RAID6 conversion, please help

[NeilBrown <neilb@suse.de>]

On Wed, 11 May 2011 09:39:27 +1000 Steven Haigh <netwiz@crc.id.au> wrote:

> On 11/05/2011 9:31 AM, NeilBrown wrote:
> > When it finished you will have a perfectly functional RAID6 array with full
> > redundancy.  It might perform slightly differently to a standard layout -
> > I've never performed any measurements to see how differently.
> >
> > If you want to (after the recovery completes) you could convert to a regular
> > RAID6 with
> >    mdadm -G /dev/md0 --layout=normalise   --backup=/some/file/on/a/different/device
> >
> > but you probably don't have to.
> >
> 
> This makes me wonder. How can one tell if the layout is 'normal' or with 
> Q blocks on a single device?
> 
> I recently changed my array from RAID5->6. Mine created a backup file 
> and took just under 40 hours for 4 x 1Tb devices. I assume that this 
> means that data was reorganised to the standard RAID6 style? The 
> conversion was done at about 4-6Mb/sec.

Probably.

What is the 'layout' reported by "mdadm -D"?
If it ends -6, then it is a RAID5 layout with the Q block all on the last
disk.
If not, then it is already normalised.

> 
> Is there any effect on doing a --layout=normalise if the above happened?
> 
Probably not.

NeilBrown