Xen users - May 2007 - Dom0 versus DomU and sata DVD drives

I have couple question about using Xen in the "real" world.

My test box is a Dell Optiplex 745 with a Core 2 processor and 4 G of
RAM.  I am using 64 bit Centos 5 with Xen 3.03.  Right now I have it
set up so Dom0 is my working domain and I add other DomU for whatever
tests i need to do.  From what I''ve read here, this is not the best
way to do things.

So my first question is, if I do an install with a minimal Dom0 and
use a DomU for my working domain, can I set it up so that DomU is what
I log on to from runlevel 5?  Is that really the best way to setup a
workstation?

Next question.  I have a sata DVD/RW drive.  Is there way to get the
DomU''s to see it?  I tried the obvious

disk = [ ''file:/xen/xp/carthagexp,hda,w'',
''/dev/cdrom,hdc:cdrom,r'' ]

for an XP install with no luck.  I''ve also tied /dev/sdc0, /dev/dvd,
and /dev/sdc with no success.  The drive does show up in Dom0.

-- 
Stephen Carville

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On Thu, 2007-05-03 at 12:03 -0700, Stephen Carville
wrote:
> I have couple question about using Xen in the "real" world.
> 
> My test box is a Dell Optiplex 745 with a Core 2 processor and 4 G of
> RAM.  I am using 64 bit Centos 5 with Xen 3.03.  Right now I have it
> set up so Dom0 is my working domain and I add other DomU for whatever
> tests i need to do.  From what I''ve read here, this is not the
best
> way to do things.
> 
> So my first question is, if I do an install with a minimal Dom0 and
> use a DomU for my working domain, can I set it up so that DomU is what
> I log on to from runlevel 5?  Is that really the best way to setup a
> workstation?
I work from my GNU/Linux desktop in dom-0 with KDE, I use Ubuntu. My
purposes are the same, having a handy sandbox in the same place I''m
making things.

Typically, I don''t set a max for dom-0, I just let dom-0 balloon to
make
way for the guests. This way I only ''shrink'' when I need to. 

If its your desktop, its just too convenient not to do (imho).

In production, dom-0 is fort knox. Nothing runs there but xen and
management tools.

You can specify runlevels, and many other things to PV guests. In
your /etc/xen directory are a bunch of really useful samples that show
these via working example. 

--Tim


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On 5/3/07, Tim Post <tim.post@gridnix.org> wrote:
> On Thu, 2007-05-03 at 12:03 -0700, Stephen Carville wrote:
> > I have couple question about using Xen in the "real" world.
> >
> > My test box is a Dell Optiplex 745 with a Core 2 processor and 4 G of
> > RAM.  I am using 64 bit Centos 5 with Xen 3.03.  Right now I have it
> > set up so Dom0 is my working domain and I add other DomU for whatever
> > tests i need to do.  From what I''ve read here, this is not
the best
> > way to do things.
> >
> > So my first question is, if I do an install with a minimal Dom0 and
> > use a DomU for my working domain, can I set it up so that DomU is what
> > I log on to from runlevel 5?  Is that really the best way to setup a
> > workstation?
>
> I work from my GNU/Linux desktop in dom-0 with KDE, I use Ubuntu. My
> purposes are the same, having a handy sandbox in the same place
I''m
> making things.
>
> Typically, I don''t set a max for dom-0, I just let dom-0 balloon
to make
> way for the guests. This way I only ''shrink'' when I need
to.
>
> If its your desktop, its just too convenient not to do (imho).
That''s pretty much how I look at it too.  I use Xen to test code or
new software on whatever version happens to be running on the target
box.  That alone has saved me a lot of time. Testing moving production
boxes to Xen is my next step.

-- 
Stephen Carville

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> I have couple question about using Xen in the "real" world.
>
> My test box is a Dell Optiplex 745 with a Core 2 processor and 4 G of
> RAM.  I am using 64 bit Centos 5 with Xen 3.03.  Right now I have it
> set up so Dom0 is my working domain and I add other DomU for whatever
> tests i need to do.  From what I''ve read here, this is not the
best
> way to do things.
>
> So my first question is, if I do an install with a minimal Dom0 and
> use a DomU for my working domain, can I set it up so that DomU is what
> I log on to from runlevel 5?  Is that really the best way to setup a
> workstation?
Hrmmm...  Well you''d still need to run X11 in dom0 in any case because
it owns
the graphics card.  You could run a fullscreen domU framebuffer login in 
here, but the GUI will not be as snappy as running it directly on dom0 - and 
you lose the ability to get any OpenGL acceleration.
> Next question.  I have a sata DVD/RW drive.  Is there way to get the
> DomU''s to see it?  I tried the obvious
>
> disk = [ ''file:/xen/xp/carthagexp,hda,w'',
''/dev/cdrom,hdc:cdrom,r'' ]
>
> for an XP install with no luck.  I''ve also tied /dev/sdc0,
/dev/dvd,
> and /dev/sdc with no success.  The drive does show up in Dom0.
There''s not currently a way to allow domUs to get full CD-ROM
functionality
without passing an entire SATA controller to them using PCI passthrough.  I 
suspect for your desktop-based testing application it''s not worth it. 
In
particular, domUs can currently only read data from a CD, they can''t
write to
it.  Also, AFAIK they can''t treat the CD as an audio disk either.

For servers, run a minimal dom0 and run all your real services in domUs.

HTH,
Cheers,
Mark

-- 
Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

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Hi Stephen,

I cc-ed this back onto xen-users, hope you don''t mind.
> > There''s not currently a way to allow domUs to get full CD-ROM
> > functionality without passing an entire SATA controller to them using
PCI
> > passthrough.  I suspect for your desktop-based testing application
it''s
> > not worth it.  In particular, domUs can currently only read data from
a
> > CD, they can''t write to it.  Also, AFAIK they can''t
treat the CD as an
> > audio disk either.
>
> That''s good enough for me and I can see the CD as read only in the
> paravirtualized linux domains.  I''ll test with RHEL4 and RHEL 3
> tomorrow.
Cool.  Paravirtualised domains don''t strictly see it as a CD at all - 
CD-related ioctls won''t work for instance.  But for many purposes this
does
not matter.
> Is there a trick to getting the CDROM to show up in XP?
I just dd if=/dev/cdrom of=/mycd.iso then export the iso file to XP.

I was under the impression that you should be able to give HVM guests access 
to the real CD-ROM drive too, but I never got that working when I tried it.  
I think in principle you just export /dev/cdrom with something like:

disk [ ... other disks ..., ''file:/dev/cdrom,hdc:cdrom,r'', ...
]

If you''re lucky it might even let the guest eject the host cd rom drive
- ISTR
seeing a patch for that at one point, don''t know if it''s
applied yet.

Cheers,
Mark

-- 
Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

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Xen-users mailing list
Xen-users@lists.xensource.com
http://lists.xensource.com/xen-users

On 5/7/07, Mark Williamson <mark.williamson@cl.cam.ac.uk>
wrote:
> Hi Stephen,
>
> I cc-ed this back onto xen-users, hope you don''t mind.
Not at all.  I would have done that myself if I''d been paying
attention...
> > > There''s not currently a way to allow domUs to get full
CD-ROM
> > > functionality without passing an entire SATA controller to them
using PCI
> > > passthrough.  I suspect for your desktop-based testing
application it''s
> > > not worth it.  In particular, domUs can currently only read data
from a
> > > CD, they can''t write to it.  Also, AFAIK they
can''t treat the CD as an
> > > audio disk either.
> >
> > That''s good enough for me and I can see the CD as read only
in the
> > paravirtualized linux domains.  I''ll test with RHEL4 and RHEL
3
> > tomorrow.
>
> Cool.  Paravirtualised domains don''t strictly see it as a CD at
all -
> CD-related ioctls won''t work for instance.  But for many purposes
this does
> not matter.
It''s good enough for now.  I only need to see a boot CD or, sometimes,
a CD/DVD with data files that need to be copied.  Eventually I may
need to create virtual desktop boxes but they won''t need a CD drive
anyway.
> > Is there a trick to getting the CDROM to show up in XP?
>
> I just dd if=/dev/cdrom of=/mycd.iso then export the iso file to XP.
Tried that but dd only copied abut 11M of the CD (MS Office).  HOwever
k3b seesm to have copied the so I can try again when IO get to work.
> I was under the impression that you should be able to give HVM guests
access
> to the real CD-ROM drive too, but I never got that working when I tried it.
> I think in principle you just export /dev/cdrom with something like:
>
> disk [ ... other disks ...,
''file:/dev/cdrom,hdc:cdrom,r'', ... ]
I''ve tried:

''phy:/dev/scd0,hdd:cdrom,r'',

but not ''file: etc.''

I''ll give that a try.
> If you''re lucky it might even let the guest eject the host cd rom
drive - ISTR
> seeing a patch for that at one point, don''t know if it''s
applied yet.
I can appreciate teh difficulty of getting a device like the CD/DVD
drive to be shared by several VM''s. I imagine the hypervisor will need
to enforce some kind of ownership of each such device.
> Cheers,
> Mark
Thank for all your help.
> --
> Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
> Mark: To answer a question with a question: What use is a skateboard?
> Dave: Skateboards have wheels.
> Mark: My wheel has a wheel!
>

-- 
Stephen Carville

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