OEM images and degraded RAID

[Roger Oberholtzer]

This may be an unusual question, but I thought it was worth asking.

It is possible to set up a raid system with one of the disks
'missing'. In such a 'degraded RAID' system, no actual raid will be
done. Or at least as long as the second disk is 'missing'.

I am curious if one could build an OEM image where the single disk is
set up this way. As long as the other disk is 'missing', it's not
doing RAID stuff. Then, after the usual install / firstboot, if
desired, a second disk could be added and the system would operate as
a RAID system. If it is possible, would the OEM image still be able to
fill the size of the disk as it can currently do? For all this, there
will only be the single OS disk present. The adding of a second disk
is after the system is all set up.

Does this make sense? I looked through the kiwi docs and didn't
recognize this kind of thing. But maybe I didn't look in the correct
place. Any pointers/suggestions are welcome!



--
Roger Oberholtzer

[Marcus Schäfer]

Hi Roger,

> This may be an unusual question, but I thought it was worth asking.

Not unusual :)

> It is possible to set up a raid system with one of the disks
> 'missing'. In such a 'degraded RAID' system, no actual raid will be
> done. Or at least as long as the second disk is 'missing'.

Yes that is how kiwi creates dm_raid capable images. As you have
only one image representing one disk you can only create degraded
raid arrays and attach/grow the array after deployment. This
works nicely

> Does this make sense? I looked through the kiwi docs and didn't
> recognize this kind of thing. But maybe I didn't look in the correct
> place. Any pointers/suggestions are welcome!

https://osinside.github.io/kiwi/image_description/elements.html
search for "degraded"

Also checkout the integration test build

https://build.opensuse.org/package/show/Virtualization:Appliances:Images:Testing_x86:tumbleweed/test-image-raid

That gives you a chance to test it in e.g. qemu with an additional
attached disk and then just add it to the array via mdadm

Cheers,
Marcus
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