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RE: [Xen-users] cant use sda on domu

To: "'Nick Couchman'" <Nick.Couchman@xxxxxxxxx>, <xen-users@xxxxxxxxxxxxxxxxxxx>, "'Holm Kapschitzki'" <holm@xxxxxxxxxx>
Subject: RE: [Xen-users] cant use sda on domu
From: "Dustin Henning" <Dustin.Henning@xxxxxxxxxxx>
Date: Tue, 25 Nov 2008 09:26:48 -0500
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        FYI, there is no booting from SCSI devices in HVM DomU because the
virtual BIOS doesn't support this.  You can have SCSI devices in HVM domUs,
but they will require drivers that may or may not exist, and once again,
they will still go through xen so it shouldn't benefit one unless due to OS
specific reasons.  Another (more obvious) exception to the above would be if
you are doing PCI passthrough instead of passing a virtual sdX (which would
presumably still require a virtual hda for booting from).

From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx
[mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Nick Couchman
Sent: Tuesday, November 25, 2008 08:26
To: xen-users@xxxxxxxxxxxxxxxxxxx; Holm Kapschitzki
Subject: Re: [Xen-users] cant use sda on domu

First, unless something has changed in 3.3, Xen does not currently support
SCSI devices in domUs.  Maybe that has changed - I'm still on 3.2, so I'm
not aware of all of the changes.  Second, you need to make sure that the
device in your domU config file match the devices you're using in fstab.  In
the domU config, you'll see something like:
disk=[ 'file:/xenstore/vmdevel/Teaming/disk0,xvda,w', ]
The xvda tells Xen that, in the domU, the disk device should show up as
xvda, so entries in /etc/fstab will be /dev/xvda1, /dev/xvda2, etc.  If you
use hda in the domU config file, then your /etc/fstab will need to use
/dev/hda1, /dev/hda2, etc.  I've never tried sda in the domU config, so I
don't know if that works or not.  All of this is if you're using a PV domU -
and with PV domUs, it doesn't really matter what you call the device in the
config file or the domU, it's going to use the Xen block device driver in
the domU to access it - you can call it whatever you like.
If you're using HVM domUs, you can only use IDE, so the devices in both your
domU config file and your guest need to be hda, hdb, hdc, and/or hdd, and
you'll need to load IDE drivers - no SCSI support in HVM, at least as far as
I know (again, could be wrong about that).

>>> Holm Kapschitzki <holm@xxxxxxxxxx> 2008/11/25 05:23 >>>

i built xen 3.3 from sources without initrd. Everything works fine, but 
i had to use with=ide creating the domu and in domu fstab i had to use 
hda instead of sda. If i use sda i get the following error:

VFS: Cannot open root device "sda2" or unknown-block(0,0) xen kernel

Its cause the kernel modules sd_mod an scsi_mod aren't build as modules? 
I build the drivers directly into kernel.


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