On Tue, 25 Nov 2014 12:01:58 +0100 cvb@kruemel.org wrote:

Hi

Am 2014-11-25 10:25, schrieb Carsten Aulbert:

quoted

Without much thinking, I would simply follow the wiki page, mark a
device as failed, remove it, repartition it, add it again, and wait
for sync to complete. Repeat for all 4 devices and finally --grow with
mdadm (followed by xfs resizing) - and of course, all online, while
machine is in flight.

That is exactoy what I did with my RAID 10 a bit more than a year ago. 
It basically worked, but there was one caveat... some part (the 
---grow?) which required a certain kernel version for which I had booted 
a live CD back then...

The thing is, I can't exactly remember what the caveat was. And as I'm 
about to grow the RAID again (having replaced all hard drives already), 
I have been looking for the related mails in the archive of this list, 
but I can't seem to find them...

So I guess we'll have to hope that Neil replies again.

I recommend creating some loop-back block devices and experimenting.

But I'm fairly sure that "far" RAID10 arrays cannot be reshaped at all.

NeilBrown