AW: [Xen-users] Use hard drive as physical mem for xen vm

["Oliver Neumann [New Identity AG]" <oliver.neumann@xxxxxxxxxxxxxx>]

I understand your point - but we need to test the application on a mysql
cluster and mysql cluster ONLY works with memory. So I have to waste all the
money to just test the application and afterwards I've got 8GB on memory I
don't need. That's what I call weird :-)

*AND* performance does not matter at all, a simple mysql query can use up to
1 hour or so, that's not bothering me. I'm just triying to save money ;-)

But I got your point, that this will obviously not work in Xen.


-----Ursprüngliche Nachricht-----
Von: Petersson, Mats [mailto:mats.petersson@xxxxxxx] 
Gesendet: Freitag, 11. November 2005 15:19
An: Oliver Neumann [New Identity AG]; xen-users@xxxxxxxxxxxxxxxxxxx
Betreff: RE: [Xen-users] Use hard drive as physical mem for xen vm

Well, I actually think that you're trying to do something that you really
shouldn't. Like Ernst said, if you haven't actually got the memory available
to do something, then it's better to let the db manager read the db-data
from the disk, than to make it believe that it's got the memory there and
cache something, which ends up being swapped in and out. You either HAVE the
memory, or you tell the DB manager that it's not got that much memory, and
let it handle this fact in whatever way it can. You get WORSE performance
from swapping than you'd get from letting the DB know that you have less
memory... Unless of course what you're trying to do is something really
weird... ;-)

--
Mats

-----Original Message-----
From: Oliver Neumann [New Identity AG]
[mailto:oliver.neumann@xxxxxxxxxxxxxx] 
Sent: 11 November 2005 14:13
To: Petersson, Mats; xen-users@xxxxxxxxxxxxxxxxxxx
Subject: AW: [Xen-users] Use hard drive as physical mem for xen vm

Hmpf, to bad. Thanks for your answer.


-----Ursprüngliche Nachricht-----
Von: Petersson, Mats [mailto:mats.petersson@xxxxxxx] 
Gesendet: Freitag, 11. November 2005 14:58
An: Oliver Neumann [New Identity AG]; xen-users@xxxxxxxxxxxxxxxxxxx
Betreff: RE: [Xen-users] Use hard drive as physical mem for xen vm

The short answer is NO. 

In longer text: Xen has no idea about swapping, which is really what you
want it to do [because you want Xen to say that there is 8GB of RAM
where there really isn't]. In Xen, all management of swapping is done in
the guest-OS, so Xen doesn't have any capability of managing swapping
[in fact, Xen itself doesn't even have a hard disk driver in it]. 

The only solution to your problem would be to have the required amount
of physical memory for the server, i.e. 8GB (+ a little bit) if you run
2x 4GB servers on one machine.

--
Mats 

-----Original Message-----
From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx
[mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Oliver
Neumann [New Identity AG]
Sent: 11 November 2005 13:52
To: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: [Xen-users] Use hard drive as physical mem for xen vm

Hi all,

I've got a machine that should serve 2 XenUs as mysql cluster nodes with
realy big memory consumption. As mysql cluster will need approx. 4GB
memory
on each XenU, I wondered if I could use hard disc space as memory for
the
XenU that appears as real physical memory within the VM. Swap is no
alternative as mysql cluster nodes check the physical memory and if that
is
not enough, they will not work.

How can I do that?

Thanks for your help!

Sincerly,
Oliver Neumann


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