Mailinglist Archive: opensuse (2224 mails)

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Re: [opensuse] Another Xen question
  • From: Hans Witvliet <hwit@xxxxxxxxxxx>
  • Date: Sun, 04 Feb 2007 01:40:53 +0100
  • Message-id: <1170549653.8169.27.camel@xxxxxxxxxx>
On Fri, 2007-02-02 at 17:11 +0000, Matthew Stringer wrote:
> I have 58 stand alone machines running Redhat 7.3
> They run shared Apache, Exim, MySQL (nothing special).
> they're all white boxes with dual P3 or P4 CPU's and local IDE disks in them.
> They form a legacy platform that means they can't really be upgraded or the
> contents migrated off any time soon.
> The problem I'm facing is that if a server fails I can't install 7.3 onto an
> new machine.
> Currently use a Suse boot CD, boot into rescue mode, format drives and install
> GRUB, then copy a 7.3 image onto drive and boot it that way (needs a little
> tweaking to get it to work).
> This worked for a while but I'm really struggling to get it to work now.
> I'm thinking of buying new machines, running SUSE with Xen. Then run RH 7.3 as
> VM's and have a SAN with external storage.
> Conceptually I can't see why it wouldn't work fine but I can't find any data
> to suggest how many VM's I can get on a server.
> For example if I have 10 dual P3 1GHz servers will they all run fine on 1 new
> server with a dual quad-core Xeon CPU?
> Hardware vendors I've asked don't seem to know for sure and I don't want to
> fork out for extra servers if they're not needed.
> Any ideas, is there a rule of thumb for working this out?
> Cheers
> Matthew

Hi Matthew,

Nice to hear ypu want to consolidate about 60 LAMP-machines based on
RH7.3. One might indeed contemplate on buying some new iron and use it
with XEN. Some thoughts however...

Did you examine the combined systemload of all those 60 machines?
How many DOM-u's are you considering to run on one machine?
If you're willing to get quad-core's the cpu-load will probably not the
problem. Memory is most likely the bottle-neck: Upto SuSE-10.0, i could
run xen-images with as little as 128MB of memory each. With 10.1 and
10.2 i noticed that during an update the systems were swapping a lott
and had to raise the memory for each DOM-u to 512MB each.
So how much memory can your (new) system hold?

Other point is, why do you want to stick to rh-7.3? Nothing against RH,
but it is certainly NOT XEN-aware, So you either need machines with VT
or Pacifica extensions, or upgrade the whole lot to a more recent
distro. (I'm not sure whether FC6 is xen-aware right-out-of-the-box)

Final point, have your xen images on a dedicated network storage, so you
can migrated dom-u's for system to system: works like a charm, and have
a real 0% down time! And use a seperate lan for it

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