Hi Daniel,
Thanks for your answer, however there are some snags...
I am using Suse Linux Enterprise server version 10.0 which supports Xen 3.0.2
where blktap is not supported, so I guess I am stuck with block devices.
Furthermore I will try to make clear what I want with the migration part:
We are an ASP company that delivers an ERP system to our users by means of
NoMachine (or GoGlobal). Sales are picking up and we have to upgrade. Now we
want to make several virtual machines that are all connected to a SAN. On the
SAN which is used with iScsi, the virtual machines are stored. However....
The SAN is located in our hosting centre, while I am at the office to create
the virtual machines. So what I want is to define a virtual machine here
locally on a server, and store that virtual machine on the SAN later when I
place the server in the rack. Is that possible?
Op dinsdag 21 november 2006 18:21, schreef Daniel P. Berrange:
> On Tue, Nov 21, 2006 at 06:15:30PM +0100, Dick Kniep wrote:
> > Hi list,
> >
> > We are going to use Xen for our virtualization effort. Now I heard from
> > some friends who are experienced Xen users that performance of the block
> > device Xen machines is MUCH better than the performance of "file based"
> > virtual machines. (is that true?)
>
> If you use blktap rather than loop devices for your file based virtual
> machines there should be minimal difference, because blktap uses
> async/direct IO to bypass the FS layer caching. You can switch to blktap by
> using 'tap:raw:' instead of 'file:' when configuring the disks. The other
> benefit of using blktap for file based disks is that it gives you much
> better data integrity upon crashes.
>
> > Now if I use a block device as a basis for a virtual machine (on LVM),
> > than it is not easy to move such a vm to another machine and make it
> > accessible by iScsi. (is that true?)
>
> If you want to migrate VMs, then you need to use a network aware block
> device such as iSCSI, or GNDB, or a shared SAN with Cluster-LVM. Of course
> same applies for file backed disks - you need to make sure the file is
> shared across all hosts to which you migrate. So either way you need shared
> storage at some point or another.
>
> Regards,
> Dan.
--
Met vriendelijke groet,
Dick Kniep
Lindix bv
De Specerij 30
1313 NE Almere
tel. 036-521 5580
fax. 036-844 1825
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