[Gllug] LVM and RAID reshuffling advice

[Kostas Georgiou]

On Thu, Nov 20, 2008 at 03:21:29PM +0000, t.clarke wrote:

> I would be AMAZED if the OS allowed you to create RAID5 with2 disks - that would
> seem to be a physical impossibility given the striping/parity method used.

You create a three disk raid5 with the third disk missing, easy to do
but you don't get any redundancy so if you don't plan to add the missing
disk right away it should be avoided.

It's mostly usefull in cases like the one that started the thread
* you add two new disks in a box with one existing disk
* create a three disk raid5 with a missing disk
* add the md in your vg
* pvmove every lv off the original disk
* remove the original disk from the vg
* add the disk to the md as the third disk
I am ignoring the /boot partition but you get the idea

Kostas
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