Re: [Xen-users] XEN 4.1.2 + gentoo-sources-3.3.0: cannot open root device sddX

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Wed, 2012-03-28 at 15:22 +0100, Flavio wrote:
> On 27 March 2012 13:55, Flavio <fbcyborg@xxxxxxxxx> wrote:
> >
> > I see that with 3.2.6 the external disk is detected as sdd (and this
> > is another issue I cannot
> > explain to myself, since the first sdX available is sdc not sdd),
> > while with 3.3.0, sometime
> > it attempts to detect as sdc...
> >
> > I am really confused.
> During the last 2.3 reboots I see the new kernel sees the disk as
> /dev/sdc ... and it seems to be OK now. Let's see how it goes.

It has been a property of Linux for quite a while now (IIRC since the
early 2.6.x days) that disks are not named in any stable or
deterministic order. So it is entirely possible that your disk will get
a different name each time you reboot, even without changing your
hardware (this is particularly true of USB attached disks but I also see
it with the SATA controllers in one of my systems).

This is not a problem which is specific to Xen, although Xen may impact
the timings of device probing etc and so change the random ordering to a
different random ordering.

If this effects you then the only way around it is to boot based on UUID
or LABEL, which requires an initramfs with udev etc. Most distros
provide tools for creating these.

Ian.


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