Xen, VT, and RAID

I'm putting together a new server that will use RAIDframe
for RAID-1 on
two drives.  I plan to run FreeBSD in an fdisk partition
using the VT
support in Xen 3.  The question is what do I do about RAID
and that
partition?  

Once choice is to do nothing, and use the corresponding
space on the
second drive for something else.  A second is to use
FreeBSD's geom
mirror on that part of both drives.  I have no idea if that
will work.
A third choice -- is there a third choice?


		--Steve Bellovin, http://www.cs.columbi
a.edu/~smb

On Thu, Dec 21, 2006 at 02:00:46PM -0500, Steven M. Bellovin
wrote:
> I'm putting together a new server that will use
RAIDframe for RAID-1 on
> two drives.  I plan to run FreeBSD in an fdisk
partition using the VT
> support in Xen 3.  The question is what do I do about
RAID and that
> partition?  
> 
> Once choice is to do nothing, and use the corresponding
space on the
> second drive for something else. 

.. such as periodic snapshots of the first filesystem,
rather than a
live mirror where you get to destroy both copies of your
data at once.

> A second is to use FreeBSD's geom mirror on that part
of both
> drives.  I have no idea if that will work.

It should, if you give it the two drives.  With a little
care about
geometery, offsets, partition names in fstab, drivers and
the like,
that may also allow dual-booting that install, either
natively on the
hardware or in a Xen HVM, while maintaining the mirroring.

There's no mirroring, but I have a usb flash stick with a
NetBSD
install on it, that I can boot natively, under HVM, or as a
domU.  The
major pain is the switch from /dev/wd0 to /dev/xbd0,
something that
doesn't affect switching a linux install between domU and
HVM since
both see /dev/hda.

> A third choice -- is there a third choice?

Hand the freebsd domU a raid1x partition from dom0, rather
than a wd0x
partition.  Other than dual-booting without Xen, is there
another
particular reason you want to use an MBR partition?

--
Dan.

On Thu, Dec 21, 2006 at 02:00:46PM -0500, Steven M. Bellovin
wrote:
> I'm putting together a new server that will use
RAIDframe for RAID-1 on
> two drives.  I plan to run FreeBSD in an fdisk
partition using the VT
> support in Xen 3.  The question is what do I do about
RAID and that
> partition?  
> 
> Once choice is to do nothing, and use the corresponding
space on the
> second drive for something else.  A second is to use
FreeBSD's geom
> mirror on that part of both drives.  I have no idea if
that will work.
> A third choice -- is there a third choice?

Yes, use raidframe in dom0 and use the corresponding raid
device for FreeBSD

-- 
Manuel Bouyer <bouyerantioche.eu.org>
     NetBSD: 26 ans d'experience feront toujours la
difference
--

On Thu, Dec 21, 2006 at 02:00:46PM -0500, Steven M. Bellovin
wrote:
> I'm putting together a new server that will use
RAIDframe for RAID-1 on
> two drives.  I plan to run FreeBSD in an fdisk
partition using the VT
> support in Xen 3.  The question is what do I do about
RAID and that
> partition?  
> 
> Once choice is to do nothing, and use the corresponding
space on the
> second drive for something else. 

.. such as periodic snapshots of the first filesystem,
rather than a
live mirror where you get to destroy both copies of your
data at once.

> A second is to use FreeBSD's geom mirror on that part
of both
> drives.  I have no idea if that will work.

It should, if you give it the two drives.  With a little
care about
geometery, offsets, partition names in fstab, drivers and
the like,
that may also allow dual-booting that install, either
natively on the
hardware or in a Xen HVM, while maintaining the mirroring.

There's no mirroring, but I have a usb flash stick with a
NetBSD
install on it, that I can boot natively, under HVM, or as a
domU.  The
major pain is the switch from /dev/wd0 to /dev/xbd0,
something that
doesn't affect switching a linux install between domU and
HVM since
both see /dev/hda.

> A third choice -- is there a third choice?

Hand the freebsd domU a raid1x partition from dom0, rather
than a wd0x
partition.  Other than dual-booting without Xen, is there
another
particular reason you want to use an MBR partition?

--
Dan.

On Thu, Dec 21, 2006 at 02:00:46PM -0500, Steven M. Bellovin
wrote:
> I'm putting together a new server that will use
RAIDframe for RAID-1 on
> two drives.  I plan to run FreeBSD in an fdisk
partition using the VT
> support in Xen 3.  The question is what do I do about
RAID and that
> partition?  
> 
> Once choice is to do nothing, and use the corresponding
space on the
> second drive for something else.  A second is to use
FreeBSD's geom
> mirror on that part of both drives.  I have no idea if
that will work.
> A third choice -- is there a third choice?

Yes, use raidframe in dom0 and use the corresponding raid
device for FreeBSD

-- 
Manuel Bouyer <bouyerantioche.eu.org>
     NetBSD: 26 ans d'experience feront toujours la
difference
--

On Fri, 22 Dec 2006 20:26:19 +0100
Manuel Bouyer <bouyerantioche.eu.org> wrote:

> On Thu, Dec 21, 2006 at 02:00:46PM -0500, Steven M.
Bellovin wrote:
> > I'm putting together a new server that will use
RAIDframe for
> > RAID-1 on two drives.  I plan to run FreeBSD in an
fdisk partition
> > using the VT support in Xen 3.  The question is
what do I do about
> > RAID and that partition?  
> > 
> > Once choice is to do nothing, and use the
corresponding space on the
> > second drive for something else.  A second is to
use FreeBSD's geom
> > mirror on that part of both drives.  I have no
idea if that will
> > work. A third choice -- is there a third choice?
> 
> Yes, use raidframe in dom0 and use the corresponding
raid device for
> FreeBSD
> 
Now I'm very confused -- I thought that I had to use an
entire fdisk
partition -- i.e., more or less a part of a raw disk -- for
VT-type Xen
domUs.  Or are you saying make that fdisk partition a RAID1
on both
drives?


		--Steve Bellovin, http://www.cs.columbi
a.edu/~smb

On Fri, 22 Dec 2006 20:26:19 +0100
Manuel Bouyer <bouyerantioche.eu.org> wrote:

> On Thu, Dec 21, 2006 at 02:00:46PM -0500, Steven M.
Bellovin wrote:
> > I'm putting together a new server that will use
RAIDframe for
> > RAID-1 on two drives.  I plan to run FreeBSD in an
fdisk partition
> > using the VT support in Xen 3.  The question is
what do I do about
> > RAID and that partition?  
> > 
> > Once choice is to do nothing, and use the
corresponding space on the
> > second drive for something else.  A second is to
use FreeBSD's geom
> > mirror on that part of both drives.  I have no
idea if that will
> > work. A third choice -- is there a third choice?
> 
> Yes, use raidframe in dom0 and use the corresponding
raid device for
> FreeBSD
> 
Now I'm very confused -- I thought that I had to use an
entire fdisk
partition -- i.e., more or less a part of a raw disk -- for
VT-type Xen
domUs.  Or are you saying make that fdisk partition a RAID1
on both
drives?


		--Steve Bellovin, http://www.cs.columbi
a.edu/~smb

On Fri, Dec 22, 2006 at 11:17:15PM -0500, Steven M. Bellovin
wrote:
> On Fri, 22 Dec 2006 20:26:19 +0100
> Manuel Bouyer <bouyerantioche.eu.org> wrote:
> 
> > On Thu, Dec 21, 2006 at 02:00:46PM -0500, Steven
M. Bellovin wrote:
> > > I'm putting together a new server that will
use RAIDframe for
> > > RAID-1 on two drives.  I plan to run FreeBSD
in an fdisk partition
> > > using the VT support in Xen 3.  The question
is what do I do about
> > > RAID and that partition?  
> > > 
> > > Once choice is to do nothing, and use the
corresponding space on the
> > > second drive for something else.  A second is
to use FreeBSD's geom
> > > mirror on that part of both drives.  I have
no idea if that will
> > > work. A third choice -- is there a third
choice?
> > 
> > Yes, use raidframe in dom0 and use the
corresponding raid device for
> > FreeBSD
> > 
> Now I'm very confused -- I thought that I had to use an
entire fdisk
> partition -- i.e., more or less a part of a raw disk --
for VT-type Xen
> domUs.

No, you can use the same kind of storage as for non-VT
guests: a physical
partition or a file

>  Or are you saying make that fdisk partition a RAID1 on
both
> drives?

Yes, that's what I meant. But it's not the only choise.

-- 
Manuel Bouyer <bouyerantioche.eu.org>
     NetBSD: 26 ans d'experience feront toujours la
difference
--

On Fri, Dec 22, 2006 at 11:17:15PM -0500, Steven M. Bellovin
wrote:
> On Fri, 22 Dec 2006 20:26:19 +0100
> Manuel Bouyer <bouyerantioche.eu.org> wrote:
> 
> > On Thu, Dec 21, 2006 at 02:00:46PM -0500, Steven
M. Bellovin wrote:
> > > I'm putting together a new server that will
use RAIDframe for
> > > RAID-1 on two drives.  I plan to run FreeBSD
in an fdisk partition
> > > using the VT support in Xen 3.  The question
is what do I do about
> > > RAID and that partition?  
> > > 
> > > Once choice is to do nothing, and use the
corresponding space on the
> > > second drive for something else.  A second is
to use FreeBSD's geom
> > > mirror on that part of both drives.  I have
no idea if that will
> > > work. A third choice -- is there a third
choice?
> > 
> > Yes, use raidframe in dom0 and use the
corresponding raid device for
> > FreeBSD
> > 
> Now I'm very confused -- I thought that I had to use an
entire fdisk
> partition -- i.e., more or less a part of a raw disk --
for VT-type Xen
> domUs.

No, you can use the same kind of storage as for non-VT
guests: a physical
partition or a file

>  Or are you saying make that fdisk partition a RAID1 on
both
> drives?

Yes, that's what I meant. But it's not the only choise.

-- 
Manuel Bouyer <bouyerantioche.eu.org>
     NetBSD: 26 ans d'experience feront toujours la
difference
--

On Sat, 23 Dec 2006 12:46:23 +0100
Manuel Bouyer <bouyerantioche.eu.org> wrote:


> > > 
> > Now I'm very confused -- I thought that I had to
use an entire fdisk
> > partition -- i.e., more or less a part of a raw
disk -- for VT-type
> > Xen domUs.
> 
> No, you can use the same kind of storage as for non-VT
guests: a
> physical partition or a file
> 
> >  Or are you saying make that fdisk partition a
RAID1 on both
> > drives?
> 
> Yes, that's what I meant. But it's not the only choise.
> 
Hmm -- ok.  There's a fair chance I'm going to stick with
the fdisk
partition anyway, to let me boot FreeBSD in native mode, but
I'll see.
(FreeBSD has better IPMI support; if I need to get at it at
that level,
I'd need FreeBSD.  Hmm -- I wonder.  I can assign the PCI
ports to the
FreeBSD domU; maybe that would work.  Hmm...  (The right
solution is
for me to port the FreeBSD driver to NetBSD, but I'm not
sure I'll have
time to do that before putting the machine into
production.))


		--Steve Bellovin, http://www.cs.columbi
a.edu/~smb