Re: [Xen-devel] incorrect disk numbering with qemu

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2014-01-16 at 12:44 +0100, Olaf Hering wrote:
> On Thu, Jan 16, Ian Campbell wrote:
> 
> > Not quite. Each xvd[a-d] creates both a PV and an emulated IDE device
> > hd[a-d], which refer to the same underlying volume.
> > 
> > This allows you to boot from hda, do an unplug and then switch to using
> > xvda.
> 
> Not really: In the end hda is connected to the emulated IDE, so today
> its really "sda" in domU because pata_piix will drive it.

true.

> sda was connected to emulated LSI SCSI.

Where did this come from? Did you request it somehow? I don't believe
there was ever an emulated SCSI controller by default.

Are you sure that this sda wasn't referring to the same backing volume
as xvda?

> But xvda was not connected to any
> emulated controller, its PV only.

Are you sure it wasn't showing up with a different name? Or perhaps by
enabling LSI SCSI you have suppressed the default IDE controllers.

>  Thats how it is done with qemu-trad.

It was not *the* way though.

> So having hda and xvda in the same config was working, and maybe even
> supported?

Maybe working, but not supported IMHO.

> With qemu-upstream this appearently changed. I'm not saying this change
> in behaviour is good or bad, just that something changed. Some people
> still use the kernel names instead of UUID or LABEL. So they have to
> adjust their config in domU and also in domU.cfg before they switch from
> qemu-trad to qemu-upstream.
> 
> 
> Olaf



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